perhaps its not the best way, but the easiest one:
if it doesn`t exist install it for that purpose :-); no kidding.
try xfce as a search term and purge all entries, one after another. it shouldn`t be to much, i just did it.
(i think if you remove thunar you`ll get removed lots of other stuff into the bargain.)
you have to check the packages if they`re just getting removed. purge them.
bout kde/kdm: dunno, seems to be that buggy way right now (i got different problems, e.g. no menu-bar in iceweasel; system-inconsistencies etc.). remove it and install another login-manager or startx from the cli. i hope those problems will be solved with some upgrades:
all as far i know, just wait if one has got a better proposal.