Setup 1 - Semi-balanced - time to complete: 1 hour 15 minutes to 3 hours.
Base party setup:
-warrior / x - tank
-mo / x - healer
-mo / x - healer
-mo / x - protection or healer
-ele / me - fire nuke
-ele / me - fire nuke
-necro / x - SS / battery
This build depends on the whole party understanding aggro real well. Note that this is only 7 party-members, i'll get to the 8th in a bit.
Group roles:
warrior / x - tank (preferably with one interrupt for siege wurms and terrorwebs)
Optimal is this not being a warrior / monk or warrior / ranger. However with the 2 pure healer monks, with no enchantment healing spells, a good warrior / monk should be able to stand his ground, though I strongly advice against it. For anything x / mo and mo / x finger of chaos dissipates enchantment, that's why wa/mo is bad. The warrior / ranger will have trouble keeping his stances up. The warrior / elementalist will be interrupted by it. The warrior / necro will make the SS go away when he is hit by finger of chaos, but this shouldnt be too much of a problem. So warrior / necro is a good choice, warrior / mesmer even better, leaving the warrior / elementalist in the middle. My preference is warrior / mesmer, with physical resistance and elemental resistance this can be the ultimate tank in the tombs.
Best Choice: Warrior / mesmer
Worse Choice: Warrior / monk, many experienced players will not party with a warrior / monk unless they know the healing monks are not using enchantments to heal the warrior (and in a pug, or a speedy group this isn't happening).
This build depends on the warrior more then most PUGs will admit, a bad lurer / tank will cause the party to fail eventually, most critical being the start of HoH, where too much aggro is easily done. The task of the other players is also very important, they have to stay out of the aggro bubble of the warrior until he has got a sticking aggro. Some people will say that the monks should be close for heal, but for all aggro to go to the warrior even they have to be out of it (hence my pref for the war/mes, they seem to be able to take more beating before needing a monk). Therefor this is a very difficult build for new players to the tombs.
mo / x - healer
A simpe healing build which preferably does not use healing breeze. The best tanks i have worked with go berserk when enchantments hit them before they go off. Apart from the chained souls there are also other enemies who use enchantment shatters (dream thingy, forgot name), so enchanting the tank will make the tank last shorter. Though some will insist on using mo / me for Mantra of resolve, the mana reserve of the monk is usually not that big, so the -4 (or more) mana that gets drained is basically one less heal spell (and in the end the same effect as an interrupted spell). So personnally I don''t really care about the subclass of the monks.
mo / x - another healer, or protection
3 healers is a good option, 2 healer and one protection is also. The benifit of the protection monk comes into play when things go wrong. A protection monk can be a real help when aggro goes wrong and breaks through the line, so that has my vote.
ele / mesmer - fire nuker
Basic and straightforward. Mantra of Resolve is a must, the big nuke spells require too long to activate and are often interrupted. Mantra of Concentration is not my favorite, my times you well get interrupted two times in a row, meaning still a failed nuke. Glyph of Renewal is also the best option for the rapid nuke, stacking Arcane Echo with is is basically overkill. The ele's should be aware not to meteor shower the one remaining grasp, the tank and SS necro can deal with him. A not so skilled nuker will mean long waits between battle for regen (even with blood ritual). For the longer fight the necro does a good job casting blood ritual on the ele's evey now and then.
Necro / x - SS / battery
Being mesmer helps this build, and it's the only character i'd recommend mantra of concentration over mantra of resolve for. Arcane Echo may help, or not if the necro gets out of mana because of it (means he can't blood ritual any energy surged monk or ele). I also recommend enfeebling blood, this skill will help alot if aggro goes bad. For secondary ranger is also good (for interrupts).
Some groups take a full battery, which is nice if you want to spend even longer in tombs, because you have to remember that with good balled up aggro SS is basically a nuke spell too. Good monks and good ele's don't need mana all the time.
The 8th party member:
-Another tank - This is what most groups do. It makes controlling the aggro easier, but takes away one slot for damage potential. So it's basically do it quicker, or do it the more careful way. This usually resolves around body blocking at certain points.
-Another ele - Means more nuking and a quicker run through tombs.
-A support char - Like mesmer or ranger. Can be good, though in my experience there has been no real need.
Setup 2 - Ranger Barrage / Pet - Time to complete: 45 minutes to 1 hour 30 minutes.
Base party setup:
-r / x - ranger with barrage and pet
-m / x - healer monk
-n / x - order necro
This is the base, i'll at to it in the different builds. But first i'll discuss the ranger.
r / x - it's very handy if 2 of the rangers are monk secondary, for the hard res. Rebirth being the best option. They also need barrage / charm animal and confort animal. Revive Animal doesn't work that good, because you need to be close for it. Throw dirt is in my opinion a must, as is at least one interrupt. Trolls unguent can also be handy, but i never bring it, my build has 0 wilderness survival

Spirits needed by the group:
-Favorable winds (there are no enemie rangers).
-Winnowing (raeally helps the barrage) - but the one bringing this needs a respectable level in WS.
Optional:
-Predatory Season - I don't like it, the +4 health isn't that good, and the one monk will be less usefull. In the build with the minion master this will make his task harder too.
m / x - The solo healer in the group, good energy management, heal party, remove hex (or inspired) are recommended. A mo / e can use glyph of lesser energy ro make heal party easier. healing breeze is also good on for this monk. Optimally the monk also keeps an eye on the pets, as they are the tanks in this group.
n / x - Order
Order of the vampire, order of pain, blood renewal and 16 blood are the key. He can also bring blood ritual for the monk, and heal party if he has monk secondary. This is the one who stays behind and spams the orders. I strongly recommend n / mo, for heal party and rebirth. His role is vital, without him the damage potential of the who group goes down so much I don't even attempt to calculate it. Well of blood is also a good skill, as blood is high already and helps out the pets.
Different barrage / pet groups
6 x ranger, 1 x monk, 1 x order necro:
Pet tanking, keeping pets alive is important, rangers and monk should keep an eye out for the pets. They are the tanks, if all pets die the enemie has basiccally broken tranks.
5 x ranger, 1 x monk, 1 x order necro, 1 x minion master necro
Pets must die, healing pets is not that important in this build. They are the food of the minion master. But they do have to be brought up again quick like in any other pet build. For the minions a balanced group is good, fiends and horrors. This is my preferred group.
5 x ranger, 1 x monk, 1 x order necro, 1 x warrior tank
The warrior tank is back, the healer must keep him alive, but this setup makes a breaking of ranks less likely.
There are many more variations on this team, some groups bring two monk, but i think that is overdoing it. A good barrage group has actually no need for a monk.
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I hope this build guide is a help to some. Please do not post comments like "OMG HE FORGOT THISANDTHAT HE IS SUCH NOOB", I have an open mind about comments and will be updating this if I find anything good. Please keep is nice. But don't come with I done it in this and that time, that has nothing to do with the build topic, unless you support it with the build.
This is not exclusive, other group builds do exist, I just haven't tried them (like the trapper build). If you know something about those builds feel free to add.
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EDIT:
-added why warrior / monks are a bad idea and a good choice / bad choice for warriors (agreeing with Racthoh).
-added affect on elementalist of finger of chaos to the warrior section (thx striderkaaru).
-and a thx to JoeKnowMo for pointing out the added ranger build stuff. I have a r / n I have been using in tombs, but I've only been using pure ranger skills. Next time I go in I'll be bringing Mark of Pain

-Timeframe for ranger build, though I have not done it as fast as some, I've adjusted the time.