Once again, Knockspell Magazine is running all old-school advertisements for free. If you have a blog, or a free module, or a website, or you're an artist (here we are a bit arbitrarily selective - you've got to be part of the old school community), or you're a retro-clone publisher, or publish materials compatible with 0e, 1e, Basic, etc ... whatever.
Email Matt Finch at mythmere at yahoo dot com with the text of a classified ad, or with a quarter-page or smaller graphic (which must contain any text you want attached). Graphic ads will need to be approved - no photos, and artwork needs to be roughly in the general style of the magazine's internal appearance. Clip art is fine.
Mythmere Games does this to show the full strength and resources of the old school renaissance, as a service to the readers, and as an expression of gratitude to those who are producing free (and paid) material for all the rest of us to game with.