I got the DR xti for DH back in March. He wants a flash unit for it. How do I know which one to get? Any suggestions would be great. The canon site was of no help. I couldn't find any flash units on there at all.

Sher

The Canon 430EX should be fine unless you need external power for multi hour use without having to worry about changing batteries.

http://www.usa.canon.com/consumer/controller?act=ProductCatIndexAct&fcategoryid=141

The 580EX has an external power connector and more power but might be overkill. It's also bigger.

You can also consider third party to save a buck. Just make sure it is ETTL-II compatible. Sigma has a powerful flash at less cost.

http://www.sigmaphoto.com/flashes/flashes_flashes_details.asp?id=3257

I don't have experience with it but I have used third party flashes before with no problem in the film days.

Some people may warn you about using non-Canon flashes fearing the electronics might harm your camera....I haven't read enough proof to agree with them.