Create cusom cards like this to show off your profile a bit differently.
Detailed achievements list with how-to info.
Let your 360 log your game playing (available as http://syndicated.livejournal.com/cmorrigu_360 )
So far, I like this achievement list the best. It has direct URLs so you can bookmark/show off the list, and plenty of stats.
Nice achievement details list, can't find direct link to mine, just use the search box.
Some achievement details, again no direct link that I can find.
Sign up for some evident benefits, not sure yet.
Blogs, stats, etc.
See new online toys here.
See (supposed) RL pics of gamers.
News, MarketPlace announcements (available as http://syndicated.livejournal.com/xbxmarketplace/ )
That's about all I've found so far.
I bought 4 Xbox Live Arcade games so far, and I grabbed Fable and Lego Star Wars for the Xbox1 the other day. I even ordered the Vision camera pack, which includes 12 month Live Gold, 3 games, and 200 points. That should be in this week sometime.