When considering a service like a web host, factor in if they have a high PR page that mentions testimonials - or even try and get your testimonial onto their homepage. The more impressive your site is, the more likely they are to use your quote to prmote their product, and in doing so link to your site.

Doing so is real easy, and a great way to get a non-reciprocal link. Here's two examples that took me a brief email each to achieve:

http://www.routhost.com/testimonials.php - PR3
(my site is GoogleFan.com)

http://www.phpwebhosting.com/sc.html - PR6
(searchenginez.com)

This technique is applicable to any web services, not just hosting. Another angle is free products/services that list customers who have made donations. A $20 donation is a nice gesture, but is also a very cheap link if the PR is high.