Hey Karen,
Welcome to TPF. This subject comes up a lot, and a search on the term flash diffusers yielded over 11 pages of hits for me
The Photo Forum - Photography Discussion Forum - Search Results
One thing to note: flash diffusers make the flash softer at close distances, and are great for such things as insects, flowers, coins, and other close-up subjects which are small. But, beyond about 10 to 15 feet, a speedlight flash that uses a slip-on diffuser, does not have anywhere near the softening effect that it does at closer ranges.
There are many products: Sto-Fen Omni Bounce, Lumiquest products of many types, the Gary Fong brand of products (numerous models), as well as air-inflatable soft boxes from PhotoFlex and other brands, and also small fabric softboxes from various manufacturers.
One person whose opinions on this subject opf flash diffusers deserve special attention is Big Mike: he answers a lot of questions about flash diffusers, and he tries to drive home the point,over and over, that a diffuser only soften light when it is a large source, relative to the size of the subject,and distance from light-to-subject. If you wade through the threads, you'll find sample photos, and a lively discussion about flash diffusers. For the record, I like StoFen OmniBounce, Nikon's own StoFen look-alike, and the PhotFlex air-inflatable soft box. As well as what is called a "bounce card",and then, umbrellas or bounced flash.