1. Grand Melee. Everyone knows that a 1v1 arena is something everyone is clamoring for. Well the grand melee takes it up a notch. Dump say 24-48 solo players into a circular arena where there is no place hide... maybe everyone is together and has a non-removable form of pacificism on them until the start of the match. When the clock starts it's every man for himself. The winner is either the last man standing or has the most kills before time runs up, where the latter you get rezzed to keep fighting. I'd love to see what'd happen when a congested battlefield gets cluttered with maelstroms and firestorms.

2. Group or Guild Grand Melee. Like thre grand melee or the tombs, but as of now, tombs is kind of designed so that 2 opposing teams will face off and they'll weed each other out. Instead, make every time fight every other team at the same time.
3. Class arena/class tombs. Similar to an arena or tombs, but there's one chevet: everyone on your team has to be of the same primary class. This can be further broken down into where your team will either be fighting another team of the same class, or your team will be fighting a team of a different class. I got this idea when I was invited into 2 tombs groups... one was all warriors one had a single ranger.
4. Solo tombs. Well, everyone wants a one on one arena, so why not a solo tombs where the best or luckiest PvPer will advance to the next round?
5. Arenas/tombs with monsters. Take some monsters, like ice imps or those imps from the ring of fire missions or those sand wurms from the desert. Put them in an arena/tombs match and have them go after groups randomly. Or if your team's flag is in the arena's single obelisk, the monsters will attack every team but yours.