Clickz has posted some tips for growing your email database. Stuff like perpetual contests, perpetual coupons, prominent opt-in boxes, and more.
People Love Stats
Here at MailChimp, we recently more than doubled our own marketing database by publishing a useful case study about writing subject lines. The best part was getting it mentioned by MarketingSherpa, but we also used PRweb to distribute the press release (for a couple hundred bucks), and got decent results there, too. If you’ve got access to lots of intriguing industry stats, publish ’em!