From Corpus Callosum: Yeah he's a psychiatrist, but what the hell...
Merck Medicus is a great site. I had to provide some medical license information, so I don't think it is available to everyone. That is annoying, but I understand why they do that. The site provides free access to resources such as Harrison's Online, Mosby's Drug Consult, etc. I assume the pay for that access, and I also assume that they would have to pay a lot more if they opened it up to everyone.
Biomed Central is a publisher of open-access biomedical journals. Some seem rather obscure to me, such as Cerebrospinal Fluid Research, but others have a wider appeal. I occasionally browse these journals just to keep myself updated, or to find things to blog about.
The Doctor's Guide to the Internet is a news aggregator that pulls in articles from a variety of sources, plus some CME programs. You can register, then customize you own page with the feeds that are of greatest interest to you. Sometimes the robots pick incorrectly, such as when it included Unexpected hemodynamic depression after induction of anaesthesia - (Anasthesiol Intensivmed Notfallmed Schmerzther) in the channel for Depression. The robots pick up a lot of case reports, which are a good way to refresh your knowledge base and exercise your clinical thinking skills.
PhRMA Medicines in Development is on online database of pharmaceuticals currently in some stage of development. I like to browse through it from time to time, in order to keep up on what is in the pipeline.