If you're interested in more general Superman / other fiction crossovers, and don't mind me pointing at my own work, I've posted several at bigapricot.org, mostly Superman Returns with some influence from L&C (e.g. my version of Ma Kent is more like L&C than Superman Returns)
http://www.bigapricot.org/cgi-bin/author.pl?Marcus_Rowland The big one there is The Return, with three sequels, which is primarily a Supergirl story.
I'll second the suggestion to look at Twisting The Hellmouth - the L&C category is
http://www.tthfanfic.org/Category-2-687/Lois+and+Clark.htm Mostly L&C / Buffy crossovers, but some others too. For the unitintiated, anything that mentions Halloween (or has the initials YAHF) refers to the Halloween episode of Buffy in which various characters took on the personality of the person whose costume they wore - in canon it was a soldier, a ghost, etc., but in fanfic it tends to be people with awesome powers who somehow retain them after the spell ends...
