Site directed mutagenesis kit

[Thomas C. Chiles]

Can anyone direct us to a kit or method that will afford site directed
mutagenesis of a gene without having to perform a lot of subcloning steps
etc.  In short, we have subcloned a gene at great time and cost into a
eukaryotic expression vector which affords expression of the gene product
in our B cell "model" lines.  We would like to change several nucleotides
within the gene while keeping it in the expresson vector.  From a novice
standpoint, 1) what is the best approach (any references?); 2) is there a
kit on the market that aid us in this endeavor?

Steve Amato, Chiles' laboratory
ChilesT at hermes.bc.edu