XP After lvl20

I've been playing a couple of weeks and I recently reached lvl20. My green experience bar filled up again but nothing seemed to happen when it got to max, it just went back to the start again. I understand that 20 is the final lvl, but are any extra skill points awarded or anything like that, or is the experience bar now completely redundant?

skill points are given each time the xp bar fills up after lvl 20...useful in the beginning but becomes unneeded later on.

ya i just removed the xp bar from my interface, didn't see a need

After level 20, skill points are pretty much only spent on crafting consumables.

Buying Signets of Capture too.

after you have all the skills (you will need skill points to get those)--both elites and reg skills, skill points are used for making consumables.
so useful at the start, but after you have been around for a while--not so usefull anymore.

http://www.guildwiki.org/Consumables list of consumables. The perfect salvage kit is very useful if you are changing armor and don't want to lose your rune of superior vigor. The Arctic Summoning stone is relatively cheap and the Kveldulf it summons can be useful doing dungeons or HM vanquishes.

Then too, you might want to buy all the skills for your main character so you can try out different builds on the fly. Skill points are very useful. You can see how many you have by pressing the "H" key.

Carrying Scrolls of Resurrection makes a good out of combat rez for the whole party. You can also sell consumable sets and components for those sets.

Additional skill points are far from useless.

Also ofcourse if your going for the legendary survivor title you need to get 1,337,500 xp without dying.
Also XP in general when in explorable areas will remove death penalty, having quests with xp is good for leveling up your heroes too just by puttin them in your party when you accept the quest reward.

I just wanna add, you can use normal skill points to buy hero skill points at a hero skill trainer. Useless if you already can change your secondary profession, but handy if not and want to but more skills for your heroes.

You also need 15 skill points to craft Envoy weapons.

Thanks all, I must admit so far I've just been using the same 2 or 3 warrior skills to kill monsters.

Another question though - have I now maxed out the number of attribute points I can get? I've been looking forward to maxing out both my hammer skills and strength but I need just a few more points.

You can check that by setting all attributes to 0. If you have 200 available points then you are maxed out. If you have 170 or 185 then you need to do one or 2 specific quests, depending on what campaign you are born in.
And remember to put the attribute points back before you go kill more monsters

Each campaign has a way of acquiring 30 additional attribute points for characters from that region. http://wiki.guildwars.com/wiki/Attribute_points