If you're looking for something different, get a Wii.
But seeing as the PS3 has a much better selection of exclusives now and in the future than Wii, I'd recommend that.

Really, it depends on which list you prefer.

MGS4, Ratchet, Uncharted 1&2, Valkyria Chronicles, Resistance 2, LittleBigPlanet, Killzone 2, GT5, God of War 3, Heavy Rain, White Knight Chronicles.

or

SSBB, Mario Galaxy, Twilight Princess, Metroid Corruption, Mario Kart, Animal Crossing, Puch Out, MadWorld, The Conduit.

Wii60 is more logical

360/DS :)

Since you don't have a HD TV a wii is the better choice.

You really need a HD TV to enjoy the maximum potential of the PS3 and indeed your beloved 360.

I have a Wii60. Great combination.
Unless you're a big fan of Sony's own games (which you probably aren't since you bought a 360) it's no use buyin a PS3. There will be hardly any 3rd party PS3 exclusives.

There are a lot of Wii exclusives out now and coming in 2009 that are very worthwhile. Zelda, Galaxy, No More Heroes, Kart, Fire Emblem, Symphonia 2, etc...
Here is a list of 2009 Wii games: http://vgchartz.com/forum/thread.php?id=34940

PC-Wii >>>>>>>>Wii60>Wii-PS3

I tells ya! Wii is very friendly to yer pocketbook!

just don't ask me why I typed it like that.

I am a Wii60 owner. Though right now the Wii gets the most use I love them both equally. Both have their cons and their pros and both have exclusive games and features you MUST check out. I see them as very different gaming experiences. The Wii is a more classic console with emphasis on fun, easy to learn gameplay but enduring replay value and innovation. The 360 is all about modern technology and its implementation in gameplay.

I will eventually own a PS3, but I am broke right now. Plus, many of its games can be found on the 360, so if I want to check out a game its likely its on the 360.

Blah.

Pick whatever you want. But based on your PS3 paragraph you don't want one, so don't get one.

Get a Wii it offers many more different titles then 360 and PS3 which overlap with most games, its also new and innovative way to play your games.