Well, after the card is formatted it can be used for all games, but should always be formatted before doing anything. After that, its free reign until you run out of space.
As for cheap games, just search around. Buying games used at places like Gamestop, Blockbuster, and EB will save you some money. Some of those places even have big sales on used games once in a while, and regular discount cards.
For good games, it depends on your tastes. A game may be geared towards your age group, but it may not be your tastes though. Same with your daughter. If you liked Prince of Persia give the second one a try. It is darker and more violent(mainly tacked on just to get sales) but is still quite a solid game.
For a short list, let me give you a list of the best stuff on the ps2.
Metal Gear Solid 3(amazing story, graphics, gameplay...especially story!)
Katamari Damacy(strangest game you can get for $20, and one of the best)
Ratchet and Clank series
Sly Cooper Series
Mercenaries
DDR Max(great game for both you and your daughter to play together too)
Taiko Drum Master(another great rhythm game)
That is just current stuff, none of the back catalog. Just so many good games on the system. If you want further help, invest in a gamecube and xbox as well. No sense in limiting your gameplay options eh?
And for some great GBA stuff, Legend Of Zelda Minish Cap. That is one of the greatest games put out on that system in the last year, or any system any year.
And this should be put in software I believe
