Can someone list all Transformers crossovers released so far? I'm mostly after GI Joe vs Transformers series, but I have no clue on how many series are out there.

This is a list of the G.I. Joe Vs Transformers series:
G.I. Joe Vs Transformers Volume 1:
#1
#2
#3
#4
#5
#6
All collected in the G.I. Joe Vs Transformers Vol 1 TPB

G.I. Joe Vs Transformers Volume 2:
#1
#2
#3
#4
All colellected in G.I. Joe Vs Transformers Vol 2 TPB

G.I. Joe Vs Transformers: The Art of War Vol 3:
#1
#2
#3
#4
#5
All collected in the G.I. Joe Vs Transformers: Art of War Vol 3 TPB

G.I. Joe Vs Transformers: Black Horizon Vol 4:
#1
#2

Hope that helps.

I just received a series of GI Joe & the Transformers (4 comics) from 1986... And I'll be getting "Divided front" (6 comics) and "Black Horizon" soon. Is DF vol. 1 or 2? Or something else?

Divided Front is a completely different series, which is not related to the others I listed. The ones I listed above (G.I. Joe Vs TF) was Devils Due Publishing's TF and G.I. Joe crossover series. Divided Front is the second volume of Dreamwave's TF and G.I. Joe crossover series.
Dreamwave's crossover series consisted of:
Transformers/G.I. Joe Volume 1:
#1
#2
#3
#4
#5
#6
All collected in Transformers/G.I. Joe TPB

Transformers/G.I. Joe: Divided Front Vol 2:
#1

And then Dreamwave went bankrupt :/ So yup, both are completely separate series' by their respective publishers.

I find all this very confusing... So far, I got :

-Marvel // GI Joe & the Transformers #1-4
-Marvel // The new Avengers vs the Transformers #1-4
-DDP/ GI Joe vs the Transformers #1-6
-DDP // GI Joe vs the Transformers II #1-4
-DDP // GI Joe vs the Transformers "The art of war" #1-5
-DDP // GI Joe vs the Transformers "Black horizon" #1-2
-DW // Transformers GI Joe #1-6
-DW // Transformers GI Joe "Divided front" #1

So what am I missing now? Also, you say there's a #6 to "Art of war" but my #5 issue says "THE END" and it doesn't look like there's a #6. And you say there's only #1 for "Divided Front" but a guy just sold me a series of 6 "Divided front" comics...

Sorry I made a mistake, Art of War was only 5 issues, and volume 2 is only 4. I'm not with it today *edits other post*
There is however, only 1 issue of Divided Front- Dreamwave went bankrupt before they could release any more. So going by your list, it seems you have them all now!

Ok, you reassured me because I got a pack of comics today and was stunned to see that I only got 1 issue of Divided Front instead of 6... Thanks for all your help!! And now I somehow have an extra series of DW TF GI Joe #1-6 (didn't know I would get it as well)... Anyone interested?

Oh, I just remembered... wasn't there an issue of GI Joe (old Marvel series?) with Transformers starring in just one issue?

No problems, glad I could help
As for Transformers in one issue of G.I. Joe, I'm afraid I'm not sure on that one :/

Just curious, but are ya'll including the G.I. Joe storyline that led into G2, as a crossover as well?

Aoi

Ahh yeah, it was 4 issues long if I'm correct? I forgot that one, thanks.

There's also smaller crossovers.

Issue #3 of the Marvel comic featured Spiderman and Nick Fury.

also Characters like Circuit Breaker and Death's Head are technically mainstream Marvel Characters that started in Transformers even though people might tell you otherwise... Don't believe them! THEY LIE! LIES I TELL YOU LIES!!!

OK, so maybe Circuit Breaker kinda saved the whole Universe before being in transformers...

OKay, now list all the damn cover variants and i'll be happy.

The UK comic featured a crossover with Dr. Who, I kid you not!

well sort of. Death's head was shunted out of the transformers universe, into the Doctor's where he was shrunk, and then sent to the main marvel universe.