Financial Times, but there are other, non-public (paid for) services that we use a lot, too. Bloomberg, Wrightson, etc...
I trade US Treasuries in the Repo Market. posted by Grither at 9:04 AM on April 30
StackOverflow.com (well, I could get away without reading anything else) posted by mkb at 9:12 AM on April 30
Foundation Center Great email alerts: requests for proposals, fundraising industry news, and links to publications in various fields tangential to the nonprofit I work for. posted by greekphilosophy at 9:41 AM on April 30
SEOmoz's blog. Great tips for content optimization and technical best practices for SEO. posted by DrDreidel at 9:43 AM on April 30
AlertNet.org Great source for public health / development news that frequently is ignored by the mainstream media. posted by charmcityblues at 9:48 AM on April 30
arXiv.org. I'm a physicist, and anything anyone writes in my field (quantum information) gets put on there for anyone to download for free. posted by zxcv at 9:51 AM on April 30
Nature via their RSS feeds and Google Reader. As well as a few other journals (Science, Genome Research, PLoS Computational Biology). posted by grouse at 10:14 AM on April 30
I (grudgingly!) read Above the Law. It doesn't help with professional skills, but it seems to be the most efficient way to keep up with conditions in my segment of the legal market. posted by grobstein at 1:25 PM on April 30
Opalesque - a summary of hedge fund related news compiled daily. The only thing it doesn't pull is potentially-relevant SEC releases (proposed rules - it will catch news/press releases), but other than that, it has amazing range. posted by mccn at 1:48 PM on April 30
posted by prufrock at 8:57 AM on April 30