Thinking about buying a video game system for the family for Christmas. But, I don't know what to get (if any)

Currently we don't have a game system at all. What I am looking for though is maybe something can can replace the Blu Ray player we currently have.

With the Blu Ray player (Sony) we can use the WiFi to watch netflix and the like as well as play DVD and Blu Ray. I just bought it a couple of weeks ago at Wal-Mart because our DVD player went belly up.

Now I am wondering if I should get a game system instead as my wife is interested in doing a workout to a video game. She is a fan of "the Biggest Loser" and saw they had a game for it. She also saw the x-box new sensor thing and thought it was pretty cool... So, I am just wondering what these game systems can do and if they are worth it...

Of course the Wii stands out because as a kid we both used to enjoy playing Mario Bros and the like. But I want to make sure I get the best for the money and the features.

So, Can they all play Blu Rays? Can they all access the internet (Netflix, YouTube, etc)? Do they all come with wireless or do they require an add-on part or a hard line?

Thanks to all in advance