After doing 200+ safety checks at a police bike auction last weekend, Sarah and I here at B!KE developed a pretty finely tuned sense of bike triage :) (which, of course, will be no match for yours after this project!)

While a positive/negative result in any of these situations doesn't necessarily mean the bike is toast, it's a good way to get a quick sense of how much work is needed - and possible to teach a volunteer who don't have strong repair skills.
+ is the frame damaged?
+ try to twist the stem with the F wheel between yer legs. While a twistable stem may just be loose, I'm always amazed at how many quill wedges have been stripped on cheaper bikes.
+ check the F + R hubs (if present) for knock
+ check the headset for loose/tight
+ check BB for knock
+ would it be hypothetically possible to turn the wheel with a chain?
+ would it be hypothetically possible to stop the bike with at least one brake (while gently coasting uphill...?)
+ general state of housing, cable, tires (if any). 

This is just what my morning brain produces, and is more or less what we were doing in the parade of sad overvalued bicycles coming out of the police auction. I think the general idea would be to make a checklist and, if you're feeling particularly organized, including details like frame type, size and colour has the beginnings of a most awesome database, then add up the number of answers one way or another to 'triage' the bike. 

I wouldn't get too caught up in trying to sort by wheel size, but if that is what makes sense to you, you could do too things:
1) Guess. most 99% of older steel road bikes 'round these parts are going to be 27 x 1 1/4, older cruisers will be 26 x 1 3/8, mountain bikes with be 26 x [decimal], etc. 
2) You could try measuring from centre of dropouts to centre of brake pads. This should (hypothetically) be half the ISO bead seat diameter number listed on the side of of the tire. 
I.e., 
27 x 1 1/4 = 630mm = 315mm from c-dropout to c-brake pad (obviously allow for some margin of error)
700c = 622mm = 311mm
and so on. 
The ones I would most focus on would be the older looking cruisers with their impossibly non-standard tire sizes!

Good luck!
Clifford McCarten
B!KE: The Peterborough Community Bike Shop
400 Wolfe St, Peterborough ON
(705) 748-6681
----------------------------------------------------------------------

Message: 1
Date: Tue, 25 May 2010 20:19:23 -0400
From: Ainsley Naylor <needleandthread@gmail.com>
To: The Think Tank <thethinktank@bikecollectives.org>
Subject: [TheThinkTank] Sorting Bicycles
Message-ID:
<AANLkTingSliDf0PTNjkVMesgfI20WFmNeajnKidvnOAU@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

hey all, here is a not-so-hypothetical question. If you had to sort a lot of
bicycles (I mean a lot, like a few thousand) how would you do it? The
purpose would be to sort them in a user-friendly way, so that in the future
you could find the bikes you need (i.e. bikes for a youth program, bikes to
sell, bikes to strip) as easily as possible. The bikes will be staying in
the same location for the most part which calls for a good sort and store
method, although dispersal of the bikes to other spaces will also be easier
if we sort them properly.

The best suggestion so far is to sort them by wheel size but these bikes
don't have their wheels attached - what a headache - so I'm looking for
other suggestions.

Thanks!
Ainsley and the FUCKIGOR bicycle collective
:)