I have the pre-II Canon 580EX and the comparable Nissin 866 Pro, and have had no negative issues with th Nissin, except that when used as a remote flash, with an ST-E2 on the camera, the Nissin is less likely to "see" the ST-E2's beam. Coupled with Jiko's recommendation, this makes the relatively less-expensive Nissin flashes seem like a good option.
I will heartily second langanderton's recommendation of Syl Arena's book! Read this book, and then one will understand Canon flashes much better. This author recommends starting with a 430EX II, if budget is a condsideration. Syl Arena does for Canonistas what Joe McNally's books have done for Nikonistas. (or is it Nikonians?)
Not meaning to stir conflict, of course! I/We use both Canons and Nikons!
Remember to buy the book (another stuff) from an affiliate who will pay a percentage to Cameralabs! Follow the link from this website.