Rudimentary Primer about types of flash available to work with your camera
- Canon-dedicated eTTL (thru the lens flash metering auto power control) automatic flash exposure and automatic adjustment of flash to suit the FL of the lens being used to take the photo
- Non-dedicated flash with photosensor in flash unit to control flash power
- Non-dedicated flash with only manual flash power settings to control flash power
For a rank flash amateur, you should get #1; #2 is also workable (but these are harder to find, as so many depend upon eTTL for their flash use. #3 is mostly for pros because getting exposure 'right' is not an automatic task; takes a flashmeter and or experiementation to get exposure at proper level.
Canon and many other manufacturers make #1
Only non-Canon manufacturers make #2 and #3
A used Canon flash at that price linked by MalVeaux is an excellent way to go...so many flash units (mostly made in China) are sold here but offer NO SUPPORT here nor are spare parts available when something even minor breaks--you throw it away and buy again!
The Canon 580EX and EL-1 are both #1 type; both can also do #2 in the Auto mode (which Canon often calls 'External' mode) . The EL-1 has only two zoom head settings for lens FL, while the 580EX has many FL settings that are automatically set to match the lens. The 580EX is more powerful than the EL-1, and used at $59 is a true bargain. 580EX is clearly a pro quality product, while the EL-1 lacks much of the flexibility and capability found in the 580EX, for example the EL-1 lacks the High Speed Sync capability which permits use of a faster shutter speed than X-sync speed.