I've been using this wrist rest for years and I love it.
Unlike the gels and pads, this one moves with you, while giving support. It's filled with small beads, so it flows into the shape that you need at the moment.
Puff it up and stand it on end so that your wrist sits in the middle when you are entering numbers on the keypad. It's the perfect height for right hand entry on the keyboard. Then slide it back to the mouse, roll it with the palm of your hand into the flatter shape you see in the picture. That's the perfect shape for the mouse.
It's very flexible, yet provides excellent support.
It also stands up to heavy duty abuse that the other types of rests don't. After years of major use, the seams in my ergoBead rest are still tight, it's lost no beads, and still provides great support! (Several keyboard gel cushions have seen the bottom of the dustbin in that time.)
Edit: Two years later I'm now on my second ergoBead wrist support and I still adore it. When I wrote the first review I'd just begun working online and using my keyboard and mouse more than ever. I bought a second ergoBead support at the time I wrote the review and I'm still thrilled with it two years later.
Imak Ergobeads Wrist Cushion for Mouse Non-Skid - Black #10174.