Adam at bierlegal.com is my lawyer and I can't speak highly enough of him. He's really really good and will explain things to you in a way he knows you've understood.
Call your local bar association; they can refer you to an appropriate lawyer. Have him review your current contract, and keep his contact info for reviewing any future contracts. Cost me about $200 last time I did this.
Large companies are less likely to let you change parts of the contract, but if a startup wants you they may.