Just packaged up my first little package to Anysoldier.com. I was going to write a letter, but I saw a listing where a particular soldier asked for paper and envelopes for her unit so they could write letters themselves, so I thought, heck, I can spare a few of those. So not only can you send letters to soldiers, you can send them materials so they can write letters, too!
Here is my original post about Anysolder.com. I don't mean to harp on it, and I certainly don't represent any particular political agenda, I just think our deployed soldiers are really deserving of some good mail. If you're inclined to use sendsomething.net, maybe you'd send off a goodwill letter through anysoldier.com, too.