Recently, I stumbled across a comic service that I've found to be surprisingly enjoyable. Wayne Cordova's Cheapo Comics is like an online 50-cent bin grab-bag service that Wayne started to help thin his collection of issues he has no desire to keep. For $5.00 (which includes shipping) you receive 8-10 comics from his collection.
I've made two purchases from him to date, resulting in most of "Wolverine - The End", a few Supergirl and the Legion of Superheroes, and a handful of other stuff, some of which I'd never even heard of before.
If the concept of a grab-bag, not quite knowing what you're going to get, is appealing, give Wayne's site a look. It's very basic. You click on a Paypal link, and ultimately receive comics. Even better, he's now implented a Spidey grab-bag, yielding a handful of Spidey-themed comics for the same price. Give it a look!