I just went through this and a genius Sprint phone rep helped me. I'll try to remember what he told me to do.
He suspected it was a particular app hanging me up. I wrote down the apps trying to download, then went to Market, Menu, MyApps, and found the apps trying to update. He had me tap one of them. If it was downloading, he had me cancel the update. He did that with each of the apps trying to download but not being successful.
After ridding myself of the downloading updates, he then had me open one of the ones he thought was okay. I opened it through Market, hit Update, and it worked. We then went through all the updates except for the suspected one. (It was Words With Friends.) We then uninstalled WWF, and reinstalled it.
Not only did this fix everything, it stopped a new big battery drain in the background due to their continually trying to download.
You said you tried cancelling them individually but it didn't work. That did for me, so maybe your problem is different. Have you called Sprint Tech Support yet? They are really knowledgeable.
MM
