Canon 430 EZ
A few years ago this was the most advanced Canon flash and it is still one of the best on the market. It has all the more and less important functions you would expect from high-end flash: over- and under-exposure +/- 3 EV in 1/3 steps, second curtain synch, stroboscopic flash up to 10 Hz, full manual mode with adjustable output down to 1/32 full power and, of course, full automatic flash control with six auto-zoom positions (24 mm - 80 mm). Flash head can be tilted 90o up and swiveled 90o right and 180o left. The control panel can be illuminated if necessary. Depending on the camera type, regular TTL or special Canon's ATTL autoflash is used. The ATTL mode uses the information about flash-to-subject distance, which is measured with short pre-flash IR burst if direct flash is used. If flash head is tilted or swiveled, the flash fires short regular burst before the picture is taken in order to assess the amount of reflected light. In older Canon models (e.g., series 600), this information was used to warn a photographer if a subject was out of the flash range. In newer models Canon engineers decided to cancel this useful function (!), claiming that the initial burst was sometimes too weak for the reflected light to be measured correctly. If they have offered at least flash confirmation signal instead, like in virtually all modern cameras, that would be acceptable. Unfortunately they have not, so you have no any information if the subject is in the flash range. This has been fortunately corrected to some extent in most modern flash/camera systems, but for a few years Canon probably had the worst flash system among major competitors. Also, although I do not know if this is the regular Canons' behavior, I noticed a tendency towards slight underexposure in most lighting situations with both my cameras (EOS 100 and EOS 50E) and flashes (430 EZ and ML 3 Macro).
The flash has a near-IR lamp to assist autofocusing in difficult situations such as low light or low contrast subjects. Thanks to that, there are virtually no difficult AF situations for Canons: they can focus swiftly on almost everything, including completely white subjects with no contrast at all or in complete darkness.
To summarize: if you have modern Canon body (EOS 50E or newer - e.g., 3, 30, 33, 300) and can afford it, go for something newer, preferably 550 EX. The EX flashes offer some new important functions such as fast-synch (flash can be used at all shutter speeds) and spot flash metering. After spot-metering, the measured values remain in camera's memory for 16 seconds during which, if exposure is made, the flash output is adjusted according to the pre-measured values. Canon also claims that EX flashes make much better use of matrix metering and are more difficult to fool with, e.g., exceptionally reflective subjects in a view field. On the other hand, if you use older EOS bodies, the 430 EZ is the best you can have for these cameras. There is not much sense in spending large money on most modern EX flashes as the camera is not able to use any of the most advanced functions. Canon do not make 430 EZ any longer, but you can probably find good deals in second-hand stores.