I've modeled a couple of hands before but haven't been too happy with the results.
I've created this with a view to a re-top and armature so the pose is as neutral as I could manage.
It's certainly not the finished article but I'm happy with some parts. The finger tips and nails have been a particular ball-ache. The angles of the digits (especially the thumb) have also been difficult.
The one great piece of advice that I most often forgot was;
Luckily, most of us have hands.
Use them as a reference :D