"C" (color) models are SirfIII (H20 C, Expedition C, Hunt C). The black and white models are SirfII, although I *think* the Go models might also be SirfIII. Maybe someone can confirm that last part.
Additionally, there are a multitude of bluetooth, mouse, and flash card 'dummy' (i.e., they transmit NMEA data only -- no screens) receivers that are SirfIII enabled. You can hook 'em up to your laptop or PDA. The chipset for these are usually clearly identified in the detailed specifications.
What about the Lowrance plotters (like GM3600c iGPS)? Would be nice to know since I'm using one on my sailing boat.
/Peter