The most important devices are:

Postscript and PDF to TIFF G4 (only B&W): -sDEVICE=tiffg4
Postscript aund PDF to TIFF LZW (only B&W): -sDEVICE=tifflzw
Postscript aund PDF to 24 Bit TIFF uncompressed -sDEVICE=tiff24nc
Postscript aund PDF to JPG: -sDEVICE=jpeg
Postscript aund PDF to PNG: -sDEVICE=png
Postscript aund PDF to HP-PCL (HP Laserjet compatible): -sDEVICE=ljet2p
Postscript and PDF to EPS: -sDEVICE=epswrite

More devices can be found in the Ghostscript documentation (http://www.cs.wisc.edu/~ghost/doc/cvs/Readme.htm#Devices)