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