What should I consider when purchasing a flash for my Nikon D7000?

I'm a really bad shopper (I over think everything) so if someone could help me narrow down how I know how well a flash will work for my camera or if someone could suggest one based on their experience, please help. I will be using it for portraits, family gatherings, baptisms, etc. I'm trying to find the best bang for my buck, also. So that might be a consideration.

Here is a comparison of all Nikon flashes
http://www.kenrockwell.com/...mpared.htm

kenrockwell swears by his SB400 and sometimes uses the SB600

I have the SB600 and SB800 and can vouch personally for either.click on each of the flashes and you will get a full review by ken

Guide number is what you need to consider

I wouldn't give two hoots for anything Ken Rockwell says - he likes to deliberately misinform.

You have two basic choices - a Nikon speedlight (which will allow TTL auto flash metering with your camera) or go for a cheaper manual flash. Nikon speedlights I recommend are the SB600 (SB800 - discontinued, but sometimes available second hand), SB700 or the most expensive SB900. These range in price from £220 to £320. Don't bother with the SB400 - it doesn't have a swivel head, so bouncing light off walls/ceilings is impossible.
These speedlights will allow you to mount the flash on camera (or off camera with a cord) and will automatically meter & fire at the 'correct' exposure - allegedly. The thing is, as with most things 'Auto' - it doesn't always get it right and can be inconsistent.

Alternatively, look for a manual flash. These are much cheaper than branded speedlights and are not difficult to work. They can be used both on or off camera (using radio triggers). A good manual flash is the Yongnuo YN560 (£60) and a reliable set of radio triggers is the RF602's (£25).

If you are looking to do portraiture, you really need to be getting that flash OFF camera. On camera flash is hard, frontal light because it is small & on axis. Bouncing an on camera flash off walls/ceilings can help, because it makes the light source larger (= softer), but this is only any good if the walls/ceilings are close enough AND are a neutral colour.

Getting flash off camera means you can modify it (make it softer, by making it larger with an umbrella or softbox) and change it's directionality, to sculpt something with light & shadow.