This is kind of cool – over at Goats, Jon Rosenberg is having an "open mic" call for an upcoming guest week:
Between Comic-con and my impending move at the end of July, I am feeling like I may not have enough time to do all the comics I need to do, so I am asking you good people for some assistance. Between now and July 14th, I will be accepting Guest Comic submissions from all comers, be you a professional webcomicker or an amateur webcomic reader.
I will pick the best entries and run them while I am in San Diego (and longer if I get enough good ones). All of the submissions will eventually be displayed on the site on a special page, so even if you're not picked you'll still get to be famous.