I'm late for work so real quick :
I just bought a Hammond M-111 for $200. I probably paid too much but I got it working after a good oiling and some TLC.
The M-100 and L-100 series are very similar and are the smaller 'spinet' sized Hammonds. Keith Emerson likes to beat up his L-100 on stage and a M-100 was used on Procol Harum's Whiter Shade Of Pale. They have shorter keyboards than the C3 and B3 (they don't go as low) and they don't have 'foldback' which give the C3 and B3 a fuller sound in the higher octaves.
The last 2 digits in a L-1xx or M-1xx just refer to the cabinet style
Here are some links to read : http://www.dairiki.org/HammondWiki/SpinetOrgans http://www.tonewheelgeneral.com/agelist/agelist.php www.ORGANSTUFF.com
(good place to get oil, parts and advice)