Waba for DOS , Java for DOS!! Also graphics I think.
FreeDOS(TM) kernel snapshots , The FreeDOS kernel site. Useful if you want to make a small DOS system.
FreeDOS Kernels, SourceForge , It seems the above site is offline, here are zip files available with the same stuff in them.
Balder , A boot floppy based on FreeDOS
Abandonia , One of the biggest dos gaming sites.
The CHAMPgames Fan Page , Classic arcade games.
Soleau Software , Some small games.
Clonk , A fun mining/tunneling game. Also windows versions.
Duke Nukem 3d , Great first person shooter.
Doom , Another first person shooter
textfiles.com , All about plain text files. More interesting than it sounds.
PSVIEW , Postscript and PDF viewer.
Net Lab for DOS , Various good programs, including browsers
DOSEmu , A DOS emulator for linux.
bCAD for DOS , 3d Modelling and Rendering