Well there's plenty out there to choose from, pretty much any sturdy knife with a full tang and a strong tip will work. Bigger blades are easier for most to get the hang of because of slower rotation and better control at farther distances.
Just off the top of my head, some popular brands are:
-Gil Hibben throwers by United
-Cold steel has a pretty good selection
-Sog has some decent looking ones
Here's a pic of some things I'm throwing right now...
The five matching blades are Gil Hibben, the spiked tomahawk is from condor, and the others are cheap no-name brands....
Tomahawks are also a lot of fun, and make great woods tools to boot ...here's a couple of mine....
^modded Rifleman from CS^
^Craftsman carpenters hatchet that I modified into this hawk-like thing.