If you're getting a PS2, I personally would suggest DDRMAX. It's loaded with a lot of really great songs, including some of my favorites, like I Like To Move It, Rhythm and Police, Spin the Disc, and Candy- it shouldn't be that expensive, either. You can also get DDRMAX 2, which has about as many songs. On the Playstation side of things, I'd suggest Konamix, and that's about it- the original DDR release for the PSX has too few songs to justify its price.