G.I. Joe crossovers

There have been multiple Transformers crossovers with G.I. Joe. By publisher:

Marvel

 * G.I. Joe and the Transformers - the 4-issue mini-series published in 1986.
 * G.I. Joe Starring Snake-Eyes and the Transformers - five issues of the regular G.I. Joe book published in 1993, featuring the return of Megatron.
 * Generation 2 - the 12-issue series published in 1993-94, featuring prominent appearances by the Joe team.

Marvel UK

 * Ancient Relics - issues of the Marvel UK G1 book featuring Action Force, the UK incarnation of G.I. Joe.

Dreamwave

 * Transformers/G.I. Joe - the World War 2 era mini-series published in 2004.
 * Transformers/G.I. Joe: Divided Front - the planned followup, of which only one issue was published.

Devil's Due Publishing

 * G.I. Joe vs. the Transformers - series published in 2004, with the Autobots and Decepticons as Cobra vehicles.
 * G.I. Joe vs. the Transformers II - series published in 2005, with time-travelling groups of Autobots and Decepticons.
 * G.I. Joe vs. the Transformers: The Art of War - published in 2006, featuring the rise and fall of Serpent O.R.
 * G.I. Joe vs. the Transformers: Black Horizon - published in 2007, featuring the coming of Unicron to Earth.