One of my colleagues is a plastic surgeon, and I've helped him out on some surgeries. I've seen it all, from ear pinning to nipple reduction. From an effectiveness standpoint, if you're not very overweight, liposuction of problem areas yield results that are perfectly realistic. Injecting the fat into areas (such as a butt lift) also yield great results. Recovery is not bad at all (except with butt-lifts you can't sit down for a few weeks). Lid lifts are surprisingly realistic-looking. Hair transplants are now done without a big scar (if you qualify). If you want a stronger chin, filler works well there.
Then you get into the "improved, but it's obvious work was done" category like rhinoplasties and tummy tucks.
Lastly, there's the "avoid because it usually looks worse" category like pec/calf/bicep implants. I would also put facelifts into this category. Seems like minor facelifts barely make any difference while aggressive ones always look bad.
I would avoid anything on the penis. Girth procedures can be very hit-or-miss with permanent deformity, and lengthening produces small changes and a very painful recovery.