I want a good but cheap flash for my nikon D3000 (and D800 in the future)?

I've ordered SB 900 but I want to buy a second flash that's quite inexpensive but good. I also want it to be compatible with Nikons TTL system and usable as a slave. I was planning to buy Nissin Di622 Mark || but a friend of mine (photographer) told me it's not strong enoug. What do you think?
Any other suggestions?

My bugdet is up to180 dollars.

Added (1). Mandingo wtf dude?

Http://photos.freeones.com/a_babes/Alanah_Rae_001/html/photo_007.shtml

Yongnuo YN-560 II
It's a great flash unit with a great price.