Shure SM57 - $100 (9.5/10)The SM57 instrument microphone is a must have for any home studio. It's an incredible value at $100, delivering crisp, clean recordings of whatever the hell you want it to. If you're still using a mic that came with your computer, go out and get one of these. It has always been excellent at recording guitar and vocal tracks. When it comes to drums, I've never used a microphone that gave me better recordings of my snare. Another little trick; throw one of these through the hole in the front of your kick facing the beater head (on top of a pillow or something). It will instantly make your kick sound punchy as fuck.
-Not terribly expensive, so owning one won't make your studio seem more impressive and costly.