Where can I find (a list?) Flashes that fit a Nikon D40 DSLR?

Where can I find (a list?) Flashes that fit a Nikon D40 DSLR?

There's a whole list in the user manual.

If you really need an external flash, the SB600 is about the best. Don't forget to buy a flash diffuser like those made by Gary Fong

Here's another good place to do research.
http://www.bhphotovideo.com/...video.com/

I was googling and found Sunpak PF30X Electronic Flash Unit (Nikon i-TTL) for Nikon D40
flashes for you.

*Small and light weight body requires only 2 AA batteries
*Guide Number (ISO 100): 100' (30m)
*TTL signals are automatically recognized just by mounting and turning on
*EV adjustment buttons enable free operations
*Auto Focus Assist Light supports focusing in low light situations

http://www.amazon.com/...003H7M0P6/