I was going to write an entire post detailing the rogue gear sets as well as where they drop. However, there is no reason to reinvent the wheel. This has already been done very thoroughly on WowHead.
This article has all of the tier sets as well as how to obtain each one. It organizes them by tier or by class. It also has all of the PvP sets.
The more I look at it, the more I think I may go with tier 6…
Another good place to check is WoW Roleplay Gear. It has a lot of gear sets that go beyond just the tier pieces and offer a lot of varied looks.