What flash is good for skateboarding photography i have a nikon d70s?

What flash is good for skateboarding photography i have a nikon d70s?

Nothing unreliable about a sb600 outdoors.It's, together with the sb-700, your best choice.

You can buy an SB600 or SB700 which will fire wirelessly (so you can put it on a lightstand & get it closer to the action) using the in camera menu & pop-up flash as commander. The advantages are that you'll have TTL (auto flash metering) and I'm pretty sure the D70s will allow high speed sync with a Nikon speedlight.

The downside is that the optical triggering from the pop-up flash might be a bit unreliable outdoors in bright conditions. Either of those flash is also very expensive (the SB600 is around £220, the SB700 around £300)

Alternatively, get a cheaper manual flash (something like the Yongnuo 560 - £60). You'll not have TTL control but manual flash output control is not difficult. Get a set of radio triggers (RF602's - £25) and you'll have reliable off camera triggering, even over distance & outdoors.

Edit: just to clarify - I've shot models on location in bright conditions & found the optical triggering system of Nikon CLS to be a little flaky at times, especially with distance, which is why I mentioned it with the SB600.