Are there any good sandbox titles on this site?
anything from simulation to strategy to RPG's, I just want to hear peoples opinions.

I myself view games like HOMM3 and Age of Wonders as "sandboxy" strategy games, since you get to build your army and conquer your own kingdom the way you want based upon whats available to you.

Caesar III
Pharaoh
Zeus

Patrician series
Port Royal series

RollerCoaster Tycoon 3 (1 and 2 don't have sandbox mode)

I can wholeheartedly recommend you those games!

EDIT: I'm sure there are more than that ;)

I would suggest Arma, as it is a large land mass, which also includes a level editor. There are many military vehicles to drive, as well as some cars, boats, planes/helicopters. All sorts of weapons, you can go into different houses....

As far as FPS games go, Far Cry 2 has a bit of sandboxy features. A bit like GTA3 in FPS format (in African wilderness instead of an urban city).

But if you are looking for some non-game which just lets you do your own thing, it probably isn't that much what you look for because most encounters are hostile, which limits how freely you can do whatever you want.

Stronghold Crusader you can do just the building in a sandbox mode, you can disable being attacked to just let you get on and do whatever you want to.