In protocol specifications
XMPP: extensible, http://xmpp.org/extensions/xep-0055.html mentions "first" (really given), "last" (really family), "x-gender", nick, email
In Pidgin
bonjour: n/a
gg: lastname, firstname, nickname, city, birthyear, gender (m/f/unspecified), online (true or ignore)
msn: none found
myspace: #if 0
novell: none found
oscar: by email address and (#if 0) by unspecified other fields
qq: none found
sametime: by "name or partial ID"
silc: none found
toc (#if 0'd): the search is for :-separated fields first, last, middle, maiden, city, state, country, email
yahoo: none found
zephyr: none found