I thought I'd throw together a quick map of the nether. I've marked all the tracks, portals and paths I know about. Portals named where my memory does not fail me.
Blue lines: Tracks with footpath underneath or above.
White Lines: Footpaths
Red Lines: Tracks without dedicated footpaths but may still be traversed by foot.
Green line: Path to Blaze Farm.
Portal exit locations:
1: Spirit temple (town)
2: Fenris
3: "Forest" temple (A bit west from Fenris)
4: "Westlands" (Even further west)
5: Floating Island
6: Grimper's House
7:
8: Snowball generator (Portal at Blaze Farm)
9: funtapaz's "northern" (now western) outpost
10: Mongoose's place
11: HoundofDarkness' far south outpost
12:
14: Skyrail
I'll try and get on soon to fill in the blanks.
EDIT: Thanks Mongoose[attachment deleted by ninja]