I got the Wii and DS because I really liked the Gamecube and GBA, but the games that sealed the deal were The Legend of Zelda: Twilight Princess for the Wii and Pokemon Diamond for the DS.
The PS3 I got as soon as the slim came out. Thought I'm not sure I would have bought it if it weren't for Enchanted Arms and the knowledge that Final Fantasy XIII, God of War III, and Gran Turismo 5 were coming out for it, the sequels to my favorite games on the PS2.