One advantage of using a database backed website is that it makes searching (or as some would call it "data mining") much easier. Though this site isn't database backed my other website LensPlay.com is. I queried that database for the best value lenses based on price and user ratings. The "Value" is simply the average user rating divided by the price.
In order to make these numbers more meaningful I restricted it to only lenses rated at least "above average" (a rating of 7.0) and I also restricted it only to lenses which had been rated by at least 15 users so any one rating wouldn't have a large effect on the outcome.
Interestingly Canon's cheapest lens, Canon 50/1.8 (in both the current "II" version and in the original version) were rated as being the best "value". It's no coincidence that most of these lenses are primes rather than zooms, since it's a lot easier to make an excellent and inexpensive prime lens than it is to make an excellent inexpensive zoom. The EF 85/1.8 is one of Canon's best lenses regardless of price and also makes it into the "best value" list.
Note that all of these lenses will tend to be less expensive lenses. Since the best a lens can possibly score is 10 and the $70 Canon EF 50/1.8 II rates better than an 8, no lens costing more than about $100 could ever beat it! You can make similar arguments about all these lenses. What this says is that you pay a lot for a relatively small increase in performance Or for specialist lenses like supertelephotos. The more expensive "L" series lenses are very good, but even though it may score a "perfect 10", a $7000 EF 600/4L IS is never going to be rated as "best value" on this scale!
|# of User
Canon EF 50mm f/1.8 II
* Canon EF 50mm f/1.8 II [LensPlay data]
Canon EF 50/1.8 II (discontinued)
* Canon EF 50mm f1.8 [LensPlay data]
Sigma 18-50mm f/3.5-5.6 DC
* Sigma 18-50mm f/3.5-5.6 DC [LensPlay data]
Canon EF 28mm f/2.8
* Canon EF 28mm f/2.8 [LensPlay data]
Canon EF 35mm f/2.0
* Canon EF 35mm f/2.0 [LensPlay data]
Canon EF 50mm f/2.5 Macro
* Canon EF 50mm f/2.5 Macro [LensPlay data]
Canon EF 28-105mm f/3.5-4.5 II USM
* Canon EF 28-105mm f/3.5-4.5 II USM [LensPlay data]
Sigma 50mm f/2.8 EX DG Macro
* Sigma 50mm f/2.8 EX DG Macro [LensPlay data]
Canon EF 50mm f/1.4 USM
* Canon EF 50mm f/1.4 USM [LensPlay data]
Canon EF 24mm f/2.8
* Canon EF 24mm f/2.8 [LensPlay data]
Canon EF 85mm f/1.8 USM
* Canon EF 85mm f/1.8 USM [LensPlay data]
Sigma 17-70mm f2.8-4.5 DC Macro
* Sigma 17-70mm F2.8-4.5 DC Macro [LensPlay data]
Canon EF 24-85mm f/3.5-4.5 USM
* Canon EF 24-85mm f/3.5-4.5 USM [LensPlay data]
Canon EF 100mm f/2.0 USM
* Canon EF 100mm f/2.0 USM [LensPlay data]
Note the values in the above table are a snapshot of the LensPlay database on December 3rd 2006. It's not real time data.