Have you ever played Cave Story? It's an awesome freeware indie "metroidvainia" style game. Well now you have the chance to pay for what was once free, with Cave Story+, for the low price of only $9.99! Act now and Steam will knock off an additional 15%, bringing the total purchase price to a paltry $8.49! But seriously this includes the enhancements made for the WiiWare version of the game and even promises future content.
The free version is available here, Steam version here, and the trailer's below: