I have a 600EX-RT, 430 EX II, and Yongnuo YN568EX. All good, but I mostly do off camera. If you are going with on camera, and on a budget, the 430 EX II is the best choice to start with. While I like the Yongnuo, I find the AF assist beam to be hit/miss (with more miss) and not even close to the center AF point. My two cents on Yongnuo is they are best for off camera work. But they are workhorses and usable. It is just the 430 EX II is a better choice for the first speedlite. Best of luck.
I agree. I have a couple of Yongnuo YN560s and they are great manual flashes. I also wouldn't hesitate to buy one or two YN565/YN568s instead of a second Canon flash, but I would definitely get the Canon as a first flash. It's less likely to have problems with current and future DSLR bodies and the warranty is there if you ever need it fixed. (Yongnuo offers a comparable warranty on their own flashes but there is no service center in the USA -- you'll have to ship it to China for repair/replacement!)