The Vivitar is a good value and so is the Sunpak 383.
However, I prefer the Canon 430-430EX or 550-580EX models because of the availability of high speed sync. There are times when you will want to shoot faster than the 1/250 second sync speed of the camera because you may want to shoot with a wider aperture for control of depth of field. With the above mentioned Canon units can do this while the Vivitar and Sunpak units force you to keep the shutter speed at or below 1/250 second.
A used 420ex model can be had for $125-150. Sure, that is more expensive than the Vivitar or Sunpak models but, I would rather have the high speed capability. Another advantage of the Canon models is that you can use the 550EX or 580EX as a master for other flash units if you desire more than one light source.
Additionally it is a bit easier to nail down varied exposure situations with TTL flash.