Here's a list of active link exchange "clubs". I don't recommend using only these services for your linking, but if you use them in combination with many of the other strategies listed here, they are a potent part of your marketing mix.

http://www.LinkMetro.com
http://www.linkmarket.net
http://www.link-vault.com
http://www.rsslinkexchange.net/?livefeed=2
http://www.linksmaster.com/
http://3waylinks.net/

There's also software like SEO Elite and IBP/Arelis that will seek out link exchange partners, but I've found this to be too labor intensive...