Hmmm, as a consumer what first brought me to the PDF market was one thing: Out of Print Products. Specifically the old TSR Adventure Design Kit. From there I went to the free section, and thence to the specials. I made a bunch of further purchases for DM's Day, and have continued coming nack since.
If you can gather enough support from PDF publishers a 'sampler CD' in Dungeon or Dragon might help. (I would recommend having samples not complete products in the CD, whet their appetites, don't satisfy them.) And by support I mean helping pay for the CD, not just okaying product.
Advertise in printed products by companies that also have PDFs. Bastion, Mongoose, Pinnacle, and Malhavoc come to mind.
One minor problem that I have had with your site I don't know if there is any solution for: Slow load times for the pages due to all the graphics. When I go to your site I often know exactly what I want, so the slow loads because of the graphics can be annoying, offering a low graphics page for dial up connections might help there.
The main thing I have been shopping for lately on your site has been fold up terrain, mostly by World Works, make sure those are seen at conventions, the darn things very nearly sell themselves once people see them. Get in contact with folks running games/demos at conventions, let them have promos of the terrain, heck make it part of any package the convention may hand out to the folks running demos.. Games like Mage Knight as well as wargames and Dungeons and Dragons.
As for banner ads, try TheMiniaturesPage.com the only site where I have clicked all their banners.
And, silly as it sounds: bookmarks. Make some type of bookmarks that folks can slip into their Players Handbook or Dungeon Master's Guide and use for indexing. Give them away at conventions. Put headings like Experience Rewards or Attacks of Opportunity at the top, and your logo along the length, every time they use the mark to open to that section they will see your logo, and trust me, they will find them useful. (I made my own set, then ended up printing a few more copies for my players.)
I hope this helps.
The Auld Grump