These guys are all about sales. They are especially good with copy. They sometimes distract onto esoteric things, but they are smart and know what they are doing selling online.
http://www.grokdotcom.com/ and particularly this article about copy http://www.grokdotcom.com/2007/10/29/copywriting-101/ or this one with links to free web resources http://www.grokdotcom.com/2008/11/13/33-free-tools-to-make-your-website-better/ or go to http://www.grokdotcom.com/archives/ and search for "top 10 online retailers by conversion rate" to get articles with monthly listings as well as some benchmarks.
Ralph Wilson (the owner, author and very good guy) gives very practical tips. Not overly sophisticated, but good advice and very practical because of that.
Jared Spool gives pretty good stuff out though mostly usability focused and not online Marketing per se
Jakob Nielson is the father of web usability. He has a lot of studies and things that are useful. He's a geek and his info is pretty good.
Another usability character involved with early Apple days has this list of bugs I like.
Random, some articles are good and some are less important, but there are a broad list of topics
This blog gives as good perspective of affiliate programs from a publishers perspective and I try to use it as my proxy to keep in tune with what publishers REALLY are thinking (I already know and accept that they are just using me, but it is mutual so I don't mind).
The classic Search site started by Danny Sullivan (but later sold I think)
Classic association of online marketers. The DMA for online.
Another search site from Jill Whalen who has been in the search space for a long time. http://www.highrankings.com/