Apropos of nothing, I suppose, but here's a quick list of recorders, sorted by their volume in cubic centimeters. I used the height x width x length specs provided by the manufacturers' web pages.
Basically, small recorders are half the volume of the medium models, which in turn are half the volume of the large units. Whether the medium units can be considered "hand held" really depends on the size of your hand.
For those interested, weight of the recorders is roughly proportionate to volume.
Small:
Olympus LS-10/11...139 cc
Sony PCM-M10...156 cc
Medium:
Sony PCM-D50...368 cc
Olympus LS-100 ...372 cc
Tascam DR-100 Mk II...428 cc
Marantz PMD661...552 cc
Roland R-26...605 cc
Large:
Sound Devices 722...1176 cc
Fostex FR-2LE...1550 cc
Edirol R-44...1753 cc
Tascam DR-680...2274 cc