If the other site's visitors are valuable enough to you, you might even offer to pay for a link. Promote your site URL offline everywhere you can. You can do the same with yours. Make sure all your employees include your Web address in their e-mail signature files. When you launch your site, add something, or hold a special activity on your site, you can generate traffic through press coverage.
Press releases are cheap, and they can produce stories in both electronic and traditional media.
Those stories send a temporary burst of visitors to you, and the leads are qualified because the respondents are interested in the topic of your release. Swap or buy banner advertisements on other sites. That can be expensive, but there are services that swap banner space on your site in exchange for displaying your banners on other sites. Swapped banners usually generate less-qualified traffic than targeted banner ads, but they cost much less. Pay commissions to affiliates who send customers to you.