I have posted this a few times before but ill post is again. If you want to see the things you buy off the marketplace before you actually buy it so you know that its worth spending money on (gamer pictures and themes for example). Then go here because it shows everthing that is available on the marketplace.
www.Achieve360points.com
it also shows other stuff like achievment details and shit.
Here are some other sites that are cool to check out.
www.Top360tag.com www.Xbox360achievements.org www.mygamercard.net www.majornelson.com www.gamertag.com