Anne Holland's Which Test Won? [1] Test your marketing instincts.
American Demographics [2] Always fascinating.

DMA Guidelines Quick Reference page [3]

Newsletter Biz: the Newsletter on Newsletters [4]

Survey Monkey [5] Do-it-yourself market research.

Constant Contact [6] Online email newsletter management service.

BtoB Magazine Online [7]A good resource for everything B2B-related

Chief Marketer [8] Lots of useful information and opinion.

Marketing Sherpa [9] A great source of marketing advice.

eRSVP [10] Online event registration management.

Brazen Careerist, the blog [11]