I use both the Lightshpere II and The Whale Tail Reporter. I prefer the Whale Tail, as it's a bit smaller, and there are more lighting options with it.
If you are serious about getting one, you may consider getting it from B&H, rather than GF, as B&H is a lot easier to deal with on returns. It's not that I had a problem with GF, however B&H has a store policy of full refund within two weeks of most purchases.
I have a third pary "lambancy" dome it works great. I can shoot directly to the subject without blowing them out.
I paid $19.99 plus shipping and it came with three other color gels. Look it up on the big auction site that everyone knows about.:biggrin:
I'll second Arcinio's suggestion. I bought a lambency diffuser with gels for 6bucks plus 15 shipping out of Hong Kong. Works well but is heavy and on a SB600 wants to pull the flash head down when you have it tilted at 45 degrees.