People who liked customizing Windows Live Messenger may have used http://www.ilovemessenger.com. That site has now been deprecated and replaced with, you guessed it: Windows Live Gallery. 

Although there isn't a ton of content available yet but you can still find some gems like the dummy emoticon (my personal favorite):
You can use it to make fun of others point of view.

If you're a busy person, you can get your own personal secretary free of charge:

And of course I have to do some cheap publicity of my own item, the Angel display picture:
Ok so I didn't create it. But I did upload it, so that's got to count for something.

With a one click install using these items is really fun and easy as long as you are signed into Windows Live Messenger.

So give the site a try and let me know how you liked it. Maybe you'll end up submitting some items of your own.