It depends on what you want to use it for. Vocals? Guitar? Bass?
A great all around mic is the Shure SM57. It's exactly the same as the SM58 but without the ball on top (which you can buy to turn it into an SM58 if you really want). Professional studios use this mic for everything. It's a very popular guitar mic, and a lot of people use them for vocals. You can pick one up for around $100.
If you want something more for acoustic instruments/vocals, I'd recommend the AKG Perception 420, or something in that price range. It's a large diaphragm condenser mic, and has a fantastic sound for the price. You can grab one for about $250. Don't expect to spend less than that if you want a half-decent large diaphragm condenser.
Again, it really depends on what you want to record, and how you're going to record it. You could have a U87, but with a terrible preamp and bad recording techniques it would sound like an MXL.