I am looking to upgrade my equipment this year. I plan on getting the "NEW" Canon 5D which I anticipate will be announced at some point this year, and am begining to look at lenses to use as well. Since this will be my first DSLR and first Canon, I thought I would start with a Canon 24-70mm f/2.8L or Canon 28-70mm f/2.8L & then a 70~200mm f/2.8L. But now I have the opportunity to buy a Canon EF 70 - 300 mm DO IS USM lens for about $400 (negotiating less still to done).

So what would you guys choose. I figure I'll buy all my lenses used off ebay or craigslist--my goal: to get both lenses for less than $500 each. But which would you guys choose and why? By the way, I do mainly landscape photography, but occasionally do commercial work.

The 70-300mm DO IS sells for over $900 used on ebay. Whoever is selling it to you for $400 is either ignorant or has a stolen lens. If you think it's legit and you can get it for $400, by all means buy it and make $500 regardless of whether you keep the lens.

Good luck on obtaining any of the L zooms you mentioned for less than $500 each. Going rate on those is usually in the $750-$1k range, used.

If you're asking which lens you should get first to go with your elusive "new 5D", then any of the midrange L zooms would be fine (28-70, 24-70 or 24-105 IS).

Be very careful buying any of those lenses in the sub-$500 price rance. The odds are quite high that the lens is stolen or the seller is scamming you. If you do buy such a bargain, insist on a face-to-face transfer, bring a friend or two with you, and make sure you get the original purchase receipt. If the seller balks at these conditions, he/she is a crook.

Yes, I agree, at that price either the lens is stolen or defective or both.

The lens does have a small scratch on the rear glass. I am told this does not affect the image quality--and I don't have a way to test this, so I'd have to take the guys word for it. It would be an in-person transaction, with an original sales receipt, so I don't think it's stolen.

Would the scratch on the rear glass be a problem?

That depends on the size and location of the scratch. If it is big enough, it will cause flaring that otherwisw would not happen. Take some test shots of the sky with the sun in various places along the edge of the frame and look for anything unusual when the sun is in one specific spot.

A rather low-tech solution to deal with small scratches is to try using a black felt pen to infill the scratch - this will most likely stop any potential flaring but is very unlikely to show up on images! I once had an ancient Pentax Takumar 135mm lens which had a small, deep scratch on the front element, black ink worked a treat - for the purists though this may be a bit too "Heath Robinson" an approach!!!