One Big Software Directory

http://dmoz.org/Computers/Software/

Software Search

http://dragon.ep.usm.edu/~yuen/search/software.htm

Shareware.com

http://www.shareware.com/

Software Archives.com

http://www.softwarearchives.com/

Tucows

http://www.tucows.com/

Professional Software Search Engine

http://www.aaasoftwaresearch.co.uk/

Software Reference Desk

http://www.refdesk.com/compsoft.html