Popular plugins:

Essentials (For usfull commands)
Pex (If you want group manager that's ok)
WorldEdit
AntiCreeper

For faction/PvP server:
- Faction Plugin

RPG servers:
- Actually I don't know any plugins here...

Survival game server:
- Hunger games
- spleef
- Self made games...

It's all up to you what you choose, but I recommend to use plugins you know, or plugins you are sure you can learn. Take contact with me if you have any questions.