I resisted Smallville fandom for a long time. I don't have any desire to see the canon, and I doubt I ever will. The only pairing that's at all interesting is Clark/Lex, and I don't actually like Clark very much. I "met" Lex through Ciceqi's crossovers, and he's very much an interesting guy caught in a canon that doesn't treat him right. If *I* had a smart, mad-scientist-y, morally conflicted character of my own, I'd give him some better storylines, I would. And the fandom mostly agrees.
There are really only two types of fic that I've been reading (btw, this is a 2008 fandom, with few exceptions): mpreg, and Kon/Conner fic. I do not apologize. :) Slash, and maybe gen. This will stay a moderately-small fandom, as I don't really have any more curiosity about it, and I'm pretty certain canon is shooting fanon and itself in the foot.
Fic:
~ Try Ciceqi's stuff, in my Author recs. I'm pretty sure I saw Lex infiltrate the X-Files page.
~ Try Shalott's stuff in general, but in specific, read: the Reconciliable Differences universe (Conner/Kon finds out who both his parents are, or at least that they both care about him, and matchmakes); Moving On, in which Lex takes over the universe and the 'verse enjoys it; Ulterior Motives, in which Superman and Lex Luthor get over themselves and have a truce. Go here:
http://www.intimations.org/fanfic/. All Clark/Lex, eventually. The RD verse becomes Kon/Tim. Slash, somewhat explicit.
~ Check the Spiderman recs in the Extremely Small Fandoms recs, for a crossover slash fic.
~ Conflicts of Interest, and Visiting Hours, by Prufrock. Check 'em out here:
http://glitterati.talkoncorners.net/fiction/index.php#sv. Lex took custody of Conner prior to his, uh, birth, and Conner is raised a Luthor. The stories are his POV, and he embarks on a quest to 1) find his mother, Clark (no, not mpreg); 2) get his mom and dad together; 3) survive Smallville. Clark/Lex, implied slash, and also Connor/OMCs.
~ Lady Ra writes some schmoopy Clark/Lex fics. Try her at
http://www.visionsofprettyboys.com/Smallville/Smallvillestories.htm. In a rare exception to my mpreg or Conner rule, these are just Alien!sex fic. I admit, I do like it when there are alien complications to having an affair. Three types of fic, then!
~ Skin Deep, by Rivkat. Read it at
http://www.rivkat.com/smallville/skin.html. Clark is Lex's "Left Hand of Darkness" fantasy. Genderbender aliens! Het, I guess, and slash; somewhat explicit. Clark/Lex.
~ Playing Banjo in Sgt. Zygote's Ragtime Band, by Aklani. Read it at
http://smallville.slashdom.net/archive/10/playingbanjo.html. Clark/Lex, alien!sex problems --> mpreg. Slash, explicit.
~ iHero, by Bernice. Read it at
http://members.ozemail.com.au/~brussell/ihero.htm. Oh, man - despite this having neither mpreg, nor Conner/Kon, and not even alien!sex, this one might be my *favorite*. Clark/Lex, slash, somewhat explicit. Lex develops, snerk, a new power. The title is a hint, ahahah. It *is* a power, and not just some metaphor, though, guys! This one is long, but it's worth it.
EDIT: Ahahah. SO, apparently there is another DCU character called "Connor," who is not at all the civilian identity of Superboy. Fine - so, I meant "Conner Kent-Luthor whatever-his-name-is-now" when I wrote this entry. Any and all Kon/Conner shorthand does not indicate slash between Connor Hawke and Superboy.