Hey Dave,
I was laughing looking at your question, because that's exactly what I personally do every day: find JV partners for my business. Here are some ways top of my head....
1) Type in keywords that you would use to search for your own webpage in the search engines. You should come up with tons of websites that are potential joint venture partners. Then, type in the keywords you would use, followed by 'newsletter', 'ezine' or some other variation after the keywords and get an even broader list.
2) Once you have a list of JV partners, type link:domain.com for those domains in Google.com (or any other search engine of your choice) and those websites, since they link to your potential joint venture partners, are also good JV prospects themselves.
3) Actually ask the people who are my current JV partners anyone they know who they think I can hook up with. You'd be surprised how helpful some of these people are, especially if they've already made some money with you in one capacity or another, via your affiliate program or via you promoting a product of theirs to your list etc.
Good luck with your JVs... :-)
Joe Kumar
30 Days To Internet Marketing Success