So once in a while you have this urge, this craving, this NEED to buy a new lens!
You've got a problem!
But don't worry, there are many photographers who are just like you and that's why there are so many different lenses for sale. The REAL problem is which lens to buy? How to hide it from the Mrs? How not to be so obvious ... how not to break the bank, well at least not too badly.
Here's a list that will help you (it helped me) - reproduced courtesy of BobAtkins.com
Canon EF 135mm f/2.0L USM - Rating 9.8, price $900. Not cheap, but a really outstanding lens.
Canon EF 200mm f/2.8L II USM - Rating 9.6. A very good lens indeed for "only" $650. The highest rated low cost "L" series lens.
Canon EF 100mm f/2.8 USM Macro - Rating 9.6, price $470. Highest rated lens under $600. Very sharp and gives 1:1 magnification.
Canon EF-S 17-55mm f/2.8 IS USM - Rating 9.5, price $1000. Highest rated EF-S series lens and one of the highest rated of all zooms.
Canon EF 85mm f/1.8 USM - Rating 9.5 and Canon EF 100mm f/2.0 USM - Rating 9.4, Two very reasonably priced ($350-$400) fast short telephoto lenses which are ideal for portrait work.
Canon EF 70-200mm f/4.0L USM - Rating 9.4, price $550. A highly rated zoom and the cheapest "L" series lens.
Tamron SP AF 17-50mm f2.8 XR Di-II LD Asph. IF - Rating 9.3, price $450. Very highly rated "general purpose" lens for APS-C sensor cameras. God wide to short telephoto range at a constant f2.8 aperture.
Canon EF 300/4L USM - Rating 9.2, price $700 (used). One of my favorite lenses and (if you can find one) a great telephoto that's affordable (and works great with a 1.4xTC too!).
Canon EF-S 10-22/3.5-4.5 USM Rating 9.1, price $690. An excellent lens which doesn't appear in the above lists because it's too expensive for the $600 list and the rating is 0.2 points too low to appear on the absolute best list. However a 9.1 rating is very good and the price is still affordable.
Sigma 50mm f/2.8 EX DG Macro - Rating 8.9, price $270. A high ratings/low cost for a 1:2 50mm macro lens.
Canon EF 70-300mm f/4-5.6 IS USM - Rating 8.9, Price $550. A very good telephoto zoom with very effective Image stabilization.
Tamron AF 28-75mm f/2.8 XR Di LD Aspherical IF - Rating 8.5, price $390. A well regarded lens at 1/3 the cost of the Canon 24-70/2.8L (rated at 9.1).
Canon EF 28mm f/2.8 (Rating 8.5, price $170) and Canon EF 35mm f/2.0 (Rating 8.7, price $230). Either one makes a good "normal" lens on an APS-C sensor DSLR.
Canon EF 50mm f/1.8 II - Rating 8.5 , price $100. Clearly the best bang for the buck.
Canon EF 28-105mm f/3.5-4.5 II USM - Rating 7.8, price $230. A good solid zoom for a very reasonable price. [Now discontinued].