What would be the best generic speed light for a nikon 5100?

I just bought a nikon 5100. Can't really afford the SB 700 or sb 900 flash… Any recommendations for a good generic or what's best for this camera?

I wouldn't recommend buying an off-brand speedlight… Just buy a genuine Nikon one - the SB-400 is only about 120 bucks new and 107 refurbished (directly from Nikon)

I have the SB700 and while it is a fine speedlight its current price of $329 is hard to justify. It's selling point is that it works with Nikon's Creative Lighting System. But to capitalize on this system you need several Nikon speedlights (they talk to each other) plus a RF control device if you wish to avoid the limits of Nikon's pre-flash communication link among speedlights. I also have what I consider to be a better buy- Yongnuo YN-467, a $78 flash that works with Nikon's ttl system meaning that when connected to the camera it communicates and knows the lens, f stop, aperature, ISO and focal length and sets its zoom and brightness accordingly. Seems to work fine although it is not as powerful as the SB700. But frankly it's easier to use. By the way, it uses 4 AA battries and for some reason recycles faster than the Nikon SB700. A third and even less expensive option would be a Manual flash (non ttl) that would require you calcuate the flash intensity and adjust the flash accordingly. If this is your only flash I would not recommend it but I use a Neewer TT560 for $37 that I use as a third strobe for 3-point lighting. It is very powerful but must be set manually. Bottom line- get the Yongnuo YN-467 if it is your only flash. Works great and as a built in reflector. But having made that recommendation be aware that for some reason a percentage of 3rd party flashes arrive DOA or die an early death. If you are concerned about that risk but don't wish to buy the SB700 consider buying online from Walmart and if it dies early just return it to the store.
By the way, Nikon's SB400 is not a good choice because it does not have the swivel range to bounce off walls as well as ceilings.