This is very broad, but if you grab a book like Four Stroke Performance tuning it will give you a pretty good answer. It really depends a whole lot on the particular motor of course, but stock cams seem to be around the 250 something mark. Full race seem to get up around 320, rally seems around the 290-300 mark, and sports fills the gaps in between stock and rally-ish. Of course lift is a whole other matter too. I think around 30% or so of the valves diameter seems to be around the go, but please note this is really really broad.
Cams also differ in how quickly they lift the valves, so it's worth noting timings at .5" lift. I believe around 200 is stock, semi race is around the 220 range and 240 is starting to get more rally style.
Please note these are all really really broad figures. The above book will tell you a whole lot, and is a great read.