The Linux Kernel Hackers' Guide, written by Michael Johnson, is a good source of general information about writing Linux device drivers. It is available from the usual Linux FTP sites, and is included in many compilations of Linux documentation.
The PC Card standard is only available from the PCMCIA association itself, and is somewhat expensive for non-members. The PCMCIA association is at http://www.pc-card.com, or:
Personal Computer Memory Card International Association 1030 East Duane Avenue, Suite G Sunnyvale, CA 94086 USA (408) 720-0107, (408) 720-9416 FAX, (408) 720-9388 BBS
An alternative is the PCMCIA Developer's Guide, by Michael Mori, ISBN 0-9640342-1-2, available from Sycard Technology, at http://www.sycard.com or:
Sycard Technology 1180-F Miraloma Way Sunnyvale, CA 94086 USA (408) 749-0130, (408) 749-1323 FAX
The PCMCIA Software Developer's Handbook by Steven Kipisz, Dana Beatty, and Brian Moore includes an overview of the PC Card standard, and descriptions of how to write client drivers. It also includes the Linux PCMCIA Programmer's Guide, as an appendix. It is published by Peer-to-Peer Communications, ISBN 1-57398-010-2.
Larry Levine has written a more general introduction to PCMCIA called the PCMCIA Primer. It is published by M & T Books, ISBN 1-55828-437-0.
Programming information for various PC Card host controllers is available from the corresponding chip vendors. Generally, data sheets are either available on line or can be ordered from each company's web site. A collection of datasheets can be found at http://pcmcia-cs.sourceforge.net/specs.