Thanks for the great tips Craig!
Another thing you can do is to visit the sales pages for the big product vendors and super-affiliates in your niche and subscribe to their lists. If they use aWeber or a number of other auto-responders, they are required to include a physical mailing address at the bottom of every email they send to their list.
Set up a database with their names and email addresses. Create a brochure describing your product and give it a stunning headline. Give the specs of your product and the URL to your affiliate page.
You might also include a short handwritten note. Mention ANY connections you may have with them. Have you promoted their stuff? Include URLs for review pages you have for their products. Include articles (URLs) you have submitted reviewing their products. Give the URLs for any videos you have posted promoting their stuff. If you've got a blog and have mentioned them or have links to their sales pages mention that. If you can convince them that your have tried to promote their products in earnest--even if you haven't sold a ton of them--they are much more likely to consider helping you out.
You can use regular snail mail, or--for the bigger guys you can use Express Mail or even FedEx. Sure, it costs a bit but even one big guy can make a huge difference. For what I call lower tier affiliates--guys without huge lists but who create pre-sell or review pages in your niche, you can create postcards announcing your launch and links to your affiliate page.
--Mike