Blue Snowball is really good mate!im going to abuy a blue snowball but now i have the buitl in mic from imac
To tell you the truth I can't tell the deference from a $30 mic and $100 mic
Then you aren't using it right. Try finding a decent condenser mic for $30.
I currently use a Shure SM7B (http://www.shure.com/americas/products/microphones/sm/sm7b-vocal-microphone). It comes in at around $400. I would suggest to most starting out that Blue Yeti is a decent mic and probably the best you're going to get for the price. Be warned though that you will likely upgrade at some point. If you buy the snowball, you'll just upgrade sooner. The Samson Co1u is also decent.