Thief

Weapon: 1-Handed Daggers
Main Damage Type: Physical, Poison
Primary Stat: LUK (Luck)
Skills: Link

Pros

+ High Mobility
+ Damage over time
+ Great at PvP
+ Theoretically extremely good DPS potential

Cons

- Melee
- May be hard to find a party for dungeons and raids due to stigma
- No party utility
- Can only provide good DPS if the player is skilled
- Hardest class to play
Bamboozler's Thief Guide: Link
Just take a look at the Strategies section of the guide where skill builds are shown. I have no experience with thief at the moment, but hopefully the information posted there is accurate.