For single flash E-TTL work, I use the Canon 430 EX (Mark I) with a 60D and a 7D. I often use it off camera either with an extension cord or using the wireless flash trigger of the 60D and 7D. This flash works great as an off camera main with the popup of the 60D or 7D as a fill for those times when you can't bring the studio with you (try a 2-1, main-fill ratio).
Available light is far and away my preferred way to shoot, but I dabble in portrait work strictly as an amateur. I like to keep things low budget which means home made PVC frames for backdrops and reflectors and cheap flash instead of studio strobes. Over the years I've collected six Yongnuo YN460-II flashes. At $40-45 each, these are fantastic for budget off-camera manual work. I love the built-in optical slave settings plus the seven position power settings.
So why six? I don't want to leave the impression that these aren't very strong. Using 2-3 umbrellas with one flash each works great for two or three subjects. But, with larger groups, it is very handy to be able to mount 2-3 flashes per umbrella then have a couple for backdrop lighting.
I don't know about the smart Yongnuo flashes, but the manual YN460 is a great option for the budget strobist. They do everything that my old Sunpak 383's did for half the cost.