Moissanite is also an option. Not as inexpensive as CZ but not as expensive as diamonds:
http://www.howstuffworks.com/moissanite.htm
But as Holly said, they have to be in 14KT gold or platinum. And AGAIN, the person receiving the gift HAS TO KNOW!! (and maybe get something that's not such a rip off pricewise as a diamond in the process ;) ).