Speedlight SB-600

General
An older flash for Nikon (the SB-700 is a newer version, with more features) but still, it can do - almost - all the things you might need

Pros/Cons 
+ great value. The cheapest i-TTL flash that can work as a remote flash
+ small, light
+ plenty of useful features (zoom, different modes)

- can't be used as a master
- button philosophy quite bad (you need to memorize combos to get some things done)
- no build-in bounce card



Intended Users

Great for:

• your first remote flash (as long as you have a camera than can use the built-in flash in commander mode)

• great as a cheap extra flash (you can't have too many of those!)

• as a single flash, suitable for most situations

Not for:

• the smallest possible (the SB-400 is smaller, although of course it has many limitations)

• if you want two flashes, one of which will be the on-camera flash, the SB-600 can't work as commander.

• if ergonomics matter a lot, the button/menu philosophy is pretty bad - but you get used to it

Final Verdict
I still have an SB-600, it's a great little flash. I'm using it almost exclusively remotely, together with an SB-800 as a master. I can definitely recommend it if you want a flash for the situations described above. But if you're serious about your photography and you think you'll be getting into flash photography a lot, an SB-700 (or even a used SB-800) is probably a better option. Not being able to use the SB-600 as a master is not exactly a deal-breaker, but it's something serious to think about.