How to remove apps from the "Purchased" list in the Mac OSX App Store?
I am running Lion (10.7.2), and there is an x just to the left of the Install / Installed button when you hover over the item in the purchased list. Click it for each App you do not want listed. I don't believe this uninstalls the App, merely removes it from the list. I did this to a program I actually wanted in the list, I don't recall even being asked for confirmation.

Now as far as getting a purchased App back onto your purchased list, that is another issue, and another question.