According to Stitch Kingdom, there are going to be a lot more cameos in Marvel's Guardians of the Galaxy than just Stan Lee. The site says that Disney sent them a full credited cast for the James Gunn-directed film, and who they all will play. It also includes a few fun surprises, including Nathan Fillion's cameo.
If you don't want to give your brain this knowledge then stop reading, because spoilers lie ahead. Here's the info they give:
Stan Lee will have his customary cameo, this time as the ‘Xandarian Ladies’ Man
- Nathan Fillion will be dolled up as ‘Monstrous Inmate’
- Rob Zombie lends his voice as the ‘Ravager Navigator Voice’
- James Gunn himself will appear in the film as one of the ‘Maskless Sakaaran.’
- Also appearing in the film, though not a cameo, is actor Fred the dog who assumes the role of Cosmo.
And here's the big one they mention… "Marvel legend Howard the Duck is somewhere to be found in the film. This inference comes from a line in the end titles that credits co-creators Steve Gerber and Val Mayerik. Whether it’s just a film/comic Peter Quill was familiar with before he was abducted from Earth or we’re about to have a new entry in the Marvel Cinematic Universe is just about anyone’s guess."
I would love it if Howard the Duck made an appearance! I seriously hope that his name just isn't mentioned. I do believe Gunn is crazy enough to add the character in there somewhere… that's if Marvel let him.