Official
These guides, written by the Spaced team for the Channel 4 Spaced website, are a really comprehensive guide to the series - and a lot better than my own efforts.

Episode One "Beginnings"
Episode Two "Gatherings"
Episode Three "Art"
Episode Four "Battles"
Episode Five "Chaos"
Episode Six "Epiphanies"
Episode Seven "Ends"

Unofficial
These fantastic guides are written by top-tv-comedy-writer-to-be, Dan Long. Nice.

Episode One "Beginnings"
Episode Two "Gatherings"
Episode Three "Art"
Episode Four "Battles"
Episode Five "Chaos"
Episode Six "Epiphanies"
Episode Seven "Ends"

SFX Network Guides
Also check out these fantastic guides in the SFX Online "Spoilers" section.