Assuming the result has to look roughly humanoid, a few ideas:
Regeneration as said, along with the elimination of aging.
Convert the pinky into a second thumb, so we have one on each side of the hand.
Make the knees and elbows into universal joints.
A second set of arms and a prehensile tail. The tail should have 3-4 digits at the end for grasping.
Move the brain into the torso, roughly where the heart is now; divide the heart into 2 or more separate pumps.
Replace most bone with something less brittle, more springy; more like wood.
Integrate a three dimensional weave of something like the strongest spider silk throughout the body to make flesh harder to tear, and a solid layer right under the skin to provide resistance to bullets and other high velocity impacts.
The ability to sense electromagnetic fields like some animals - probably quite useful in a society that makes heavy use of electrical devices like ours.
Better color vision; more varieties of cones, extending into the ultraviolet. The ability to perceive light polarization as well. Larger, more sensitive eyes; not having the brain in the head makes it possible to have larger eyes.
A much better olfactory sense; plenty of room for that with the brain moved.
A pair of curved (sort of like a ram’s) convoluted horns; the convolutions are in part to shape sound as they are ultrasound sonar organs like bats; the convolutions serve the same purpose as the funny shape of bat’s faces. Their other function is to serve as cooling organs and protection for a set of infrared spectrum eyes tucked in the inward curve of the horns.
Skin that can change color like an octopus (better than a chameleon).
A partially dampable pain sense with a hard cap on how bad pain can be.
A hard limit on how bad suffering of any kind can be; there’s simply no practical point in suffering that incapacitates someone.
Make everyone a hermaphrodite. Testicles are internal; some mammals have them that way so we know it’s possible.
Reproduction requires an active effort of will, and automatically shuts down if the person feels coerced (as in rape).
If impregnated, the person has the conscious choice of bringing the offspring to term or having the early-stage embryo fragment into stem cells that are scattered across the body and allowed to grow in place as new, young tissue. This allows for immortality and evolution at the same time.