Depends on if you are going to do more to the engine such as: Compression, Bore or stroke, Bore and stroke, Mild ported head, Race ported head, etc......
If you don't think you will go crazy in the future but already have a good exhaust, intake mod w/filter and some gearing, a mild cam would be a good mod to accentuate the stock engine. Something like a Yoshimura Stage I cam. I used one on a stock 2001 Hayabusa and it ran really good with Brock's GEN III exhaust, intake small mod, BMC Race filter and a 16t front sprocket.
You can get any Yosh, Web or Megacycle cams out there. Keep it mild and it will net you decent HP. Nothing crazy mind you but a nice bump.
I have a Yosh Stage 1 cam set right now. Thinking of selling it as I am building a bigger engine.