yeah theyre great little devices for the money, considering the Pocket Wizrards are like $250+.
as for flash modifiers, there's tons of them. each has a different purpose. it just depends what youre subject is. there's diffusors, bounce heads, snoots, colored gel filters to match the ambient light, etc etc. the list is endless.
i currently have these in my arsenal:
Omnibounce (i dont really like the results of this)
Lumiquest Quik Bounce (this is great for portraits, and anywhere you want to bounce your flash but dont have a surface (outdoors, churches with tall ceilings, etc)
simple white bounce card (this is integrated into my SB-900, you can use something like a business card or posterboard. this gives a nice catchlight in a person's eyes)
gel filters (these come with my sb-900 as well. these are cheap and can be found lots of places. they let you match the color of the flash with the ambient light, so you dont get any weird white balance issues)
Gary Fong light sphere (these are also popular, never used these before)
ring flash (good for portraits and macro work, never used one either)
softbox (i have two of these from CowboyStudios. dirt cheap, $35 each