A game of numbers - filling the funnel

There are quite a few ways to fill the top of the lead funnel.  Here are some key focuses for now:

• SEO - arguably the most important right now as more and more people are searching online vs. following advertising (paid search on or offline) or word of mouth (although, I believe word of mouth is the most important so this, too, is important to nurture)
• Ease of registration - this is right up there with SEO - after people hit the site, it's imperative to make it easy for people to give up their information.  Typically SFDC needs last name, email, and company to create a lead.  Vendors like DemandBase can back fill information based on shorter modified forms making getting info even easier.  The important things: compelling people to give up their info - why should they care about x offer?  Making registering easy (long forms with weird CAPTCHA and other hurdles are not excellent).  Giving people what you promised - saying they're going to get a download and giving a whitepaper (vs. product) is a flip move and can result in more opt outs.
• List purchases - there are MANY places to purchase email and phone number lists online; a few of the top dawgs include: Harte Hanks, MarketOne, Leadmaster, Catapult, and Target 250 (who focuses on FSI).  These companies price on a handful of models including double opt in email only (can be $1.50 - $3), phone verified (can be $20 on up), and pre-qualified phone prospected (can be $25 on up).
• List crawls - there are a handful of vendors in India and across the US who will manually "crawl" common forums where people have their information (Linkedin, Zoominfo, etc.).  I'm on the fence with list crawls - it feels like a shady way to get leads and find people's information, but today it's legal.
• List trades - depending on a companies privacy policy, companies can trade and share lists.  Typically the privacy policy lets people share lists when the email offer is of interest to someone on that list - this is pretty hard to measure.
• Partner programs - my favorite way to get semi-qualified leads right now is partner programs.  We've done a few recently with other technology partners who have a similar audience but complementary (vs. competing) solution and these have yielded highly qualified sales leads - a few of whom we're now in conversations with working towards a close.