Don't trade it in period unless you sell it to someone directly for a decent price it's not worth it. Trade values suck on game machines.
As far as the systems themselves. I have about 30-40 good games on my Wii, and a good 20 or so Ps3 exclusive games as well.
I like RPG's and Platform games (and especially combo's) though.
This list of PS3 games is too long to run through but quick highlights.
The Ratchet and Clank Games
Demon souls (almost worth having a PS3 for all by itself)
Infamous (and soon part 2)
Uncharted 1 and 2 (and soon 3)
3d dot heros
Disgaea games
FF13
GoW 3
GoW compilation
Heavy Rain
Little Big Planet (And soon part 2)
Resistance FoM 1 & 2
There are of course other good Ps3 exclusive games, and quite a few I prefer on the Ps3 to the xbox 360. For me though it's an easy choice since I don't pay for Xbox live....so I play all my online games for free through my ps3. I use the xbox 360 mostly for exclusives or if a game is on sale only for the xbox.
The Wii though is a great system and you can get a used one fairly cheap right now. If you use craigslist etc you can get a used Wii for less then $100 at this point (Ebay not so much do to S&H etc...might as well get a new one at that point). The Wii has tons of party games, light gun games, some really great platform games and a decent selection of RPG games as well. The list is way to long for that system, and sadly you have already missed out on some of the best deals I have ever seen on Wii games. My library of Wii games went from around 20 to around 50 over the last 3 weeks, with almost all the games (No more heroe's 2, Red Steel 2, Mushroom Men etc) costing $10 or less (some only $5 because of %50 of the second game deals).
To list the games I got would take to long but a quick list:
Shiren
Kings story
Tales of Symphonia
Muramasa
Dragon quest Swords
chocobo dungeon
punch out
House of the dead overkill
Resident evil 4
Resident evil umbrella chronicles
Metroid prime 3
Metroid other M
Mario Kart
Sin & punishment
Mad World
Just a few examples. There may still be deals going on at places like Toys are us (They had some woppers) and Amazon seems to have them fairly regularly. Walmart also had some great deals. Now would be the time to pick things up if you can. A Wii system is a great investment if you have money to pick up a bunch of games for $10 or so right now...were talking thousands of hours of games.
Don't trade in y our Ps3 though...keep it. If you don't have the money for now then you won't have the money to buy games anyway. If you do have money for games, but them now and save up for the system later....(buying them at $10 etc) as the price won't get lower then that and you can just wait to have the system you need. Look for a good deal from a friend or someone who lives near you on craigslist and you'll be set