For some people, taking a picture is all they want.  If the camera and lens can do that, then it's good enough.  For others that are a little more choosey, it's not.  You want the best lens that money can afford.  Then there are those of you like me in the middle.  I want the best lens for the money I have.

You're in luck.  Canon has gone through many iterations of most lenses and have the older models that are no longer in production but can be found here on Ebay.  Getting a good deal is easy when people don't know what they're listing.

The Canon 50mm lenses are a couple that you need to look at.  The 50mm mkI F1.8 is actually more expensive than the MkII as Canon skimped on the newer version to make it cheaper.  The mkI is worth about $80 more than the mkII.  As you move up to the F1.4 you're looking at about $100-150 more than the mkI.

The Canon 28-135 Image Stabilized (IS) lens is a wonderful lens and I have shot with it for several years until I replaced it with an L lens.  The previous version of it, the 35-135 3.5-5.6 is also a really good lens but is no longer produced.  The 35-135 was the first ultrasonic motor (USM) lens made by canon and although, it's old, it still takes great pictures.  It should be about $200 less than it's IS brother.

Be careful of the 75-300 lenses that Canon has made.  People still buy them not knowing that they're not that great.  If you're looking for a cheap alternative to an expensive telephoto lens, look at the 100-300 lens.  The only exception to the 75-300 lenses is the newest, the 75-300 IS lens.  This is a decent lens mainly because it added image stabilization.  This lens will cost $200-250 more than any of it's predecessors.

You may also be looking at a fisheye or an ultra wide angle lens.  Sigma makes a 14mm lens that is significantly cheaper than the Canon 15mm, however, make sure if you want a fisheye that you are buying a fisheye as not all wide angle lenses are fish eye lenses.  Some are rectilinear lenses that will allow straight lines to remain straight as you would see them normally.

If you're looking for Canon L lenses, then you already know that they are expensive.  A question you are undoubtedly asking is "Are they really worth the cost?"  The short answer is, "It depends on what you want."

The Canon 17-35 2.8L is a wonderful lens.  I carry it myself and use it almost exclusively for day to day shooting.  It has been replaced by the 16-35 2.8L.  Granted it is a better lens, but it is also several 400-500 dollars more.  If you still think that's too much, you may look for the 20-35 2.8L.  Be aware that Canon has just announced a new set of lenses including a 16-35 2.8L mkII.  This should be available in April 07 and will drive the cost of the 16-35 mkI down.

Canon came out with a 24-70 2.8L that is used by professional photographers everywhere.  If you don't want to spend all your hard earned money on one, you should look for the 28-70 2.8L.  This version should run you about 300-400 dollars less than it's modern equivalent.  If you can find it, Canon originally made a 35-80 2.8L that should again, be somewhat cheaper.  I've only seen one or two of these on eBay so they aren't around much.  It's still a decent lens and would probably be worth a couple hundred dollars less than the 28-70L.

The Canon 80-200 2.8L was replaced by the 70-200 2.8L.  The 80-200 is painted black and cannot use the dedicated Canon Teleconverters but it still is an awesome lens.  It's built like a tank and costs about 300-400 dollars less than the newer equivalent.  It does not have the ability to override the focus when in autofocus mode as its newer equivalents do.

The 70-200 F4 now comes in an IS version.  Be aware that IS feature will add significant cost to a lens.  The F4 IS will be approximately $400-500 more than the original non-IS lens.

Please be aware that all the prices I've mentioned are ebay prices.