Temple of Elemental Evil (which includes module T1: The Village of Hommlet -- note that unlike the later A1-4 and GDQ1-7 "supermodules," the T2-4 portions of T1-4 were never published separately) starts characters at 1st level and theoretically takes them up to around 8th level. The Slavers series as originally published (modules A1, A2, A3, and A4) was a series of tournament dungeons for characters of levels 4-7. The "supermodule" A1-4 version attempted to tie this series into T1-4 and accordingly bumped the level of the module up to, IIRC, 7-11. I don't have this version of the module, so I don't know what was changed to justify the higher level-rating, but conventional wisdom declares the originals superior to the revision. G1-3 (Against the Giants), D1-2 (Descent Into the Depths of the Earth), D3 (Vault of the Drow) and Q1 (Queen of the Demonweb Pits) were originally published as an epic series and thus tie-in together naturally. The "supermodule" GDQ1-7 version also attempted to tie the series in with A1-4, but the attempt was weak (I do have this one).
Personally, if you want to run a 1st ed module campaign starting with Temple of Elemental Evil and ending with Queen of the Demonweb Pits, I'd recommend skipping the Slavers series and in its place (between T1-4 and G1) inserting modules S4 (Lost Caverns of Tsojcanth) and WG4 (Forgotten Temple of Tharizdun), which are already a matched set (by location, not plot -- WG4 isn't really a "sequel" to S4 as such), are more appropriate to the level-range of characters who finish ToEE (level 6-10, IIRC), and also are (like ToEE and the GDQ series, and unlike the Slavers series) written by Gary Gygax, and thus feel more aesthetically "of a piece" with the rest of the sequence.
So the series would go like this:
T1-4: Temple of Elemental Evil (lvl 1-8)
S4: Lost Caverns of Tsojcanth (lvl 6-10) and WG4: Forgotten Temple of Tharizdun (lvl 6-10)
G1-3: Against the Giants (lvl 8-12)
D1-2: Descent Into the Depths of the Earth (lvl 9-14)
D3: Vault of the Drow (lvl 10-14)
Q1: Queen of the Demonweb Pits (lvl 10-14)
Oh, and one last thing -- honesty compels me to mention that module Q1 (which was actually written by the late David Sutherland, not Gary Gygax, though Gygax was given a co-writer credit in the published version) actually kinda sucks, and will almost certainly seem like a huge letdown and anticlimax after all those other, better modules. I'd actually recommend stopping after D3 (which is very open-ended and includes lots of room for individual DM expansion), but I realize that after a quarter-century the "full GDQ series" has attained such legendary status that obviously players won't be satisfied with stopping "before the end," even though they probably should be...
