Well, if you don't mind the snarkiness (as in, it's this reviewer's job to dis Smallville as much as humanly possible), Television Without Pity offers recaps of each episode.
A good, somewhat none biased site is TV.com . It used to be TVTome.com.
I didn't check out all the episodes, but starting with the last on of Season 4 and working backward, it appears that they do have re-caps of each of the episodes.
James, who, after reading some of the season 4 stuff, is glad he stopped watching the show...
Yeah, I'd go with James' suggestion if you are looking for recaps to supply you with factual data about what happened to whom and when during a specific episode. Zoom and Television Without Pity don't necessarily recap for objective accuracy but rather with the intention of looking for things to make fun of. This tends to make their recaps rather lopsided.