Untold Tales of Spider-Man: I think this was a 25 issue run, so with annuals this should make a nice 2 volume set.
Honestly, I think this could make for 1 volume if you don't mind the thickness. I usually aim my volumes around 30 issues each.
Slingers: Issues 0-12, plus the Identity Crisis storyline that led into it.
Green Goblin: 13 issues, which seems small for a volume. Can't really think of what else to add except the good Goblins first appearance in Spectacular Spider-Man.
You could include Web of Spider-Man 125 and Spectacular Spider-Man 225, which introduced him. Also, there was an issue he tied-in with when the Spidey comics became Scarlet Spider. That could help. And lastly, a loose tie-in is the Spider-Man: Legacy of Evil oneshot. Phil's barely in it but it details Ben Urich's research of all things Green Goblin. He writes a story about it and in the end he gives it to his nephew, Phil to read. Phil, of course, went on to become the Green Goblin after that.
You could also throw in the first arc of the Runaways' second volume with Phil in it (though he doesn't become the Goblin) and the Loners mini that also had him in it. Just some thoughts.
Spider-Man 2099: I was originally thinking of making this pure S-Man, with his main series,
2099 Unlimited and
Spider-Man meets Spider-Man 2099. But I've been wanting to get
Ghost Rider and
Doom 2099, so this will probably turn into Marvel 2099.[/QUOTE]
Yeah, I had the same problem. I just wanted an X-Men volume but then remmebered how much I liked the other titles up to Fall of the Hammer... then how I liked the President Doom story. Then I just decided to do a 2099 run chronologically.