Best flash for its money? Nikon D5000?

Ok so I need to be honest, I don't know very much about flashes yet, however I'm learning very quickly that I need to by a more serious flash, because the one that comes installed in camera does not cut it! I would definitely prefer to not spend too much money, however I'm guess it'll probably run me around $700. I sure would love a lower price though! I want to experiment with some fisheye lenses and it would be nice to be able to take more successful photos in shaded areas. I have a D5000. Can I have a serious photographer's advice?

It might be if it cost so much money

$700 is a HUGE budget for a single flash unit
I have the Nikon SB-600 and SB-800, and the SB-600 is perfect for nearly anything you are doing. It is simple to use, lasts a good while on fresh batteries, and is pretty powerful.

here are some good rundowns of all the Nikon flashes
http://www.kenrockwell.com/....htm#tests

at the bottom you will find a link to their pages.

I have the SB600, but it has been discontinued.

Your best options are the SB700 or SB900. For your camera, the SB700 at around $330 or so would be a good fit.

Unless you are looking for a Macro flash; the R1C1 Macro is indeed around $700. But it doesn't sound like macro is your need (and the macro flash isn't very good for general purpose flash work).

No normal flash will be able to illuminate the field of view of a fisheye lens.

Myself, i use a combination of one Nikon flash (SB-600, discontinued and replaced by the SB-700) and manual off camera yongnuo flashes. Since you likely want to use TTL on the camera, i'd chime in to the choir of those who recommend the SB-700, albeit there are third party flashes that offer TTL on the camera as well. E. G. The Yongnuo YN465.

Best bang for buck?

Metz 50 for Nikon, about $225. The only thing it doesn't have that the pricier Nikon units have is the extended reach on the zoom head. Metz goes to 105mm, the newer Nikons do 200.It will work as a slave in a Nikon CLS remote flash system.

Sigma also makes very good units for Nikon, at much lower prices. There are two models, with equal flash power but different bells and whistles. The 630 ST is only about $150, where the 630 DG Super is about $250. The Super includes high speed sync and master flash abilities.