Actually, Centos is a (free) straight clone of RedHat, minus the proprietary logos and the paid support.
You can try a few of the distros from the top 10 or 20 at http://distrowatch.com/
. Many have a LiveCD version ie you just boot off the CD and try it without(!) touching your HDD. Obviously it'll be a bit slower from the cd, but its a good way to see what it looks like.