First off, if you want to see some good salary comparisons for the fields in question, the last issue of the Hem-Onc Newswire has a good article for that. Basically, medical oncologists can probably do the best, ranging anywhere from the low $200's to upwards of $800k. Of course, that's geographically speaking - more $$$ in the midwest, and best in the south when also figuring in reimbursement rates. Rad onc is excellent also. However, the standard deviation for med onc is far greater than rad onc, so you're liable to generally start higher and maybe top out lower in rad onc, but there's less variation in that field. Surg onc kinda blows for what you do. 5 years general surgery, 2 years surg onc, and you average about $270k b/c you can do a lot of lengthy surgeries and not get reimbursed that much.
Finally, of course, if you do academic medicine, you won't make squat - probably in the $120-160k range or so. Granted, it's all relative, so if you think that's a good salary, I guess it's not so bad.
Hope that helps.