What sort of games do you enjoy? Are you into action games, first-person shooters, RPGs, time-management games? Are you a casual gamer, or hardcore?
The Wii is great for casual gamers, who don't care that much about the graphics. There aren't many of the "hardcore" games on that system - mostly "No More Heroes" and "House of the Dead 2 & 3". Some great casual games in the time-management genre (my wife's favorite), like "CakeMania" and "MySims". There's also the "Cooking Mama" series, which is more of an action game, using cooking instead of jumping and running (try filleting a tuna, then cooking and draining rice, then wrapping specific sushi and sashimi recipes - all against a timer!).
The XBox 360 and Playstation 3 are both more for hardcore gamers, although they both have casual games as well. (I'm a big fan of Worms and Worms 2: Armageddon on the XBox.) The only edge that PS3 has is the built-in Blu-Ray player, if that's at all important to you. The only really interesting exclusive on either one is Halo 3 on the XBox, and Killzone 2 on the PS3.
All three systems are backwards-compatible with the last-generation iteration of their consoles; on the Wii, you can also download most of the titles for the NES, Super Nintendo, and N64 consoles - for a price, of course.
The Wii is the least expensive of the three, and the PS3 is the most.
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Sodium is a metal that reacts explosively when exposed to water. Chlorine is a gas that'll kill you dead in moments. Together they make my fries taste good.