I think Washington, DC Art News runs one of the most gracious services around, which is the posting of opportunities for artists.
As a gallery I see they also offer seminars for emerging artists “on many areas not covered by any art school curriculum that we know of“. What a great thing.

When I think about pre-Internet days, which wasn’t that long ago, finding out about opportunities for exhibits, grants etc. was really kind of a sleuthing experience. I remember spending hours at our public library because someone there saw to receiving and filing such information for public consumption.

Yes, luckily there has always been the organizations like NYFA and [like I mentioned a few days ago] here on the other side of the woods Artist Trust that have really excelled in using the Internet, but it is nice to see someone catching those one offs that might not be known otherwise.

Here is my shortlist [undoubtedly W. coast heavy]:

a-z art
grants
art access bulletin
art deadlines list
artdish-opps
artist resource 
artist resource network
artist trust-late breaking
art space
betty bowen
calls for entry-p.n. art
centrum
nsf antarctic artists program 
nyfa
office of arts and cult. affairs
seattle artists
seattle pub library-informed artist
volunteers in parks
wla- arts legal clinic