Need 300mm zoom?

I am looking for a ?-300 zoom for my active amature use. I cannot afford a prime 300mm L but still need something pretty sharp and a zoom (I think) will provide me the most flexibility. I would love it to be a Canon but can accept an off brand. And it needs to work with film and digital. And $$ is important.

Any and all suggestions greatly appreciated. Links to comparisons etc all help. Can't find anything that makes sense to me using Google - just mostly 'ad' info. Many thanks

ADDED NOTE: I have a cosina 28mm-210mm which is not sharp at either end but it 'works'. Need something better under $500(?).

How much? A 75-300mm F4-5.6 USM pops to mind, probably around $150-160 - I didn't think it was that good, but it works and is good value for money.

Adam, I am looking at between $300 and $400 US, lower end better but best quality in price range is what I want/need. Thanks

I think the Sigma 70-300 APO would be great for you.
Its also better quality than the Canon according to a lot of people who have used both

The Sigma 70-300 APO or Canon 100-300 pop to mind as great budget alternatives, great bang for the buck. If you could weasel a bit more into your budget (yes I know this exceeds it) the Canon 70-300 IS might be a great choice.

The Sigma 100-300 f/4 is also well regarded.

I've recently bought a Tamron 70-300 tele-macro for £120 ($220ish) which had really good reviews on a lot of sights. Added bonus of macro although its only 1:2 ratio it suits me for flowers, etc.

My english is getting worse!!! Sites not sights

If you're willing to go just a bit over 500 (ie $550ish), you can grab the Canon 70-300 IS which is reputed to have really good IQ which comes close to L lenses.