Besides the resources already mentioned I have a few different sites I check out.
I get a daily newsletter from eMarketer.com. Usually two short articles reviewing some research and surveys. Every week there's an interesting article or two.
I also regularly skim the following sites:
E-Commerce News: E-Commerce
ECommerce-Guide to New Products, Trends and Market Research
Ecommerce Articles, News and Tips for Online Retail - Get Elastic Ecommerce Blog
I'm sure there are some better sites out there but these and everything mentioned above seem to keep me up to speed pretty well.