I haven't had too much experience with 3rd party flashes on my Nikon... but I'm happy with my flash exposure using my Speedlight.
Some comments read about 3rd party flashes mention inconsistent flash metering.
* also, my Speedlight is CLS-capable without any additional accessories.
I'll say . if you're using Nikon , you should know that nikon makes the best flash systems .
next you should know that nikon has wireless TTL through its CLS systems.
next you should know that you pay for what you get.
i have used 3rd party flashes. some are good some are so-so. one thing about 3rd party is that the quality degrades over time . i dont know how to explain but more like sometimes you will get inconsistent shots . I'v owned the Sunpak PZ40x and tried the PF30x and both are so-so .
get an sb600 the very least .
if you've got the D70,80/90 , you can use your built in flash as a commander mode to fire the Sb600 in CLS . otherwise you need at least he sb-800/900 on the d40/40x/60/5000 to do the same.
the sb-800 and 900 can both used as master flash but not the sb-600