Is there a mounted flash that is compatible with Nikon D3000?

The on camera flash isn't so great (as a lot of you will know) and I'd like to practice taking some photos of my friend, but it will be pretty gloomy outside. Just in case I need some extra lighting, I thought I would look in to an alternative. Any pointers? As mentioned above, this is for a Nikon D3000 and I was thinking of renting one to try out first.

Sigma EF-610 DG Super or DG ST.

Both fully Nikon TTL compatible, will work great on your D3000, and cost about half what the Nikon flashes do.

Any of the Nikon flashes will work like the SB600, SB700, SB800, SB900.

Of course, any non-TTL type flash will work in manual mode.

Using a diffuser or off-camera flash with modifier (e.g.umbrella) will be helpful.