My collection of Godzilla comic books spans from the 1977-1979 Marvel series to the recently defunct Dark Horse series.
The Marvel series ran for 24 issues and featured Godzilla interacting with the Marvel Universe and battling a whole new crop of Marvel monsters. Most G-fans were not too pleased with Marvel's interpretation of the King of the Monsters. I don't think they represent the best comics have to offer, but the series has it's own unique charm. I'll post some more in-depth reviews of the series in the future (I have to go digging in the closet to find it first).
Dark Horse began publishing Godzilla comics in 1987. Since then they have published a few one-shot books and featured Godzilla stories in some of their anthology series. They even released an english language manga version of Godzilla (1984). Their on-going Godzilla series lasted 16 issues in 1995-1996. Gamera joined Dark Horse for a four issue series in 1996 which was loosely tied into the film Gamera Guardian of the Universe. As far as I know Dark Horse still plans to do more Godzilla and Gamera comic books in the future.