What are some basic plugins I need for a server?

Essentials (everything that comes with it)
PermissionsEX
GriefPrevention (you can create a square of large protection, and within it you can create subplots so players can only building side that subplot)
WorldEdit

Im going to poke a little at what nsuugaming said.

Essentials Groupmanager is unstable, unreliable, and overly not very fluid.

Here's my list:
Essentials
Essentials Spawn
Essentials Chat
Essentials AntiBuild
Permissions EX (It's a most flexible and stable permissions manager) DO NOT USE CHAT MANAGER THAT COMES WITH IT IF USING ESSENTIALS CHAT
ModifyWorld (it comes with PEX)
HawkEye to keep track of who places blocks and griefing
WorldGuard
WorldEdit
Orebfuscator (Anti Xray Mod)
Disguisecraft is a fun one that doesn't change much.

CombatLog is a good combat logger plugin.

Nametags can be done wiiithhh... Dispnamechanger and/or Narrowtuxlib. I'm not so sure about the latter one.

Otherwise all those other ones are great, too.

I'd recommend using :-

Essentials
Essentials Chat
Essentials Spawn
Essentials GroupManager (If you want user groups, for the colourful name tags)
WorldEdit
WorldGuard
CoreProtect or Hawkeye (Closes your gonna get to the xray plugin you want)
and Multiverse Core if you're planning to use multiple worlds.