I'm jumping ship to Ambush Alley.
Think of it as what Call Of Duty would be like on the tabletop.
I 'gained' a copy of the rules online (It can be downloaded on the main website as a PDF) and you can use any miniatures you want to represent models.
Models are divided into four classes that represent how good they are (From armed civillians to SAS dudes).
The main 'competitors' to Games Workshop would be : WarMachine/Hordes(Two different flavours of armies that are at war with each other, you can use Horde armies in Warmachine for example), Infinity, BattleTech (Prepainted Robots, it can be either very basic or extremely detailed depending on how you want to play, allegedly), Flames of War (World War 2 based), Heroclix (Pre-painted mini's from just about any comic series I think... I've seen Freddy Krueger and Wolverine before, so I have no idea how vast it is. I think they do Heroclix Star Wars too) and Malifaux.
As for other games:
Wikipedia has you covered.
I'm tellin' ya, it feels so good to not see SPACE MARINES everywhere anymore, that was seriously beginning to give me a headache...
Anyway, good luck in your searches!