There are just so many keyboards out there — if you're looking for just a small number of models, you could miss so much. Sound/feel is sadly the only useful guide, as pulling keycaps won't really help — there are so many interesting switches to be recognised.
Here's a brief list, though:
Monterey K101/K102 — always seem to be blue Alps
Monterey K104 and K108 — interesting switches in those
Monterey K110/SIIG MiniTouch/SIIG SunTouch Jr
Ortek MKB-84 SX/MCK-84 SX (the white Alps versions)
Chicony KB-5981 (SMK switches and Windows keys)
Chicony KB-5591 (SMK switches, and trackball)
KPT KPT-84 (nice little 75% with various switches)
NMB RT-8XXX* (and many but not all RT-10X as some are dome)
Various others here with blue Alps:
http://deskthority.net/wiki/Alps_SKCM_Blue#Keyboards — NTC KB-6151 and KB-6251 are pretty hit and miss, though the *EA models should be Alps (but won't all be), since *EM seems to be Mitsumi, and *EN may be for "NTC switch" (Alps clone — another company that pretended the clones were their own, unless Nan Tan owned Himake at some stage).
It gets worse, though, as there are loads of keyboards that aren't all that exciting (KPT, Podworld, Oriental Tech, Micronorth etc) but have Tai-Hao Alps-mount doubleshots that are worth ten bucks just for the keycaps if they're in good condition.