The electoral-vote.com website currently has a very thorough
breakdown of what's going on with the Senate primaries, including
dates of States with upcoming primaries, and write-ups of all the
places where the primary is likely to matter:
http://www.electoral-vote.com/...
In general, I'm a big fan of "electoral-vote.com", which is run
by a computer scientist named Andrew Tannenbaum (Linus Torvalds
supplied a pull-quote for his book on operating systems: "This
book changed my life!"). During election season, this one guy
hanging out in Europe typically does a better job of coverage
than the entire US media. And he's been doing poll aggregation
since before Nate Silver made it cool:
http://www.electoral-vote.com/
Tannenbaum points out that the the two primaries in March aren't
at all in doubt, the real fights begin in May. And all of the
fights are on the Republican side (a common theme is
establishment vs. tea-baggers, I'm sure you'll be shocked to
hear). The Democrats have already settled on their candidates,
so if you're a true-blue Democrat these primaries are hard to
care about... myself I've always been willing to switch party
affiliations to vote in a primary I was interested in, but these
are different times, and my nose-clothespins might not be strong
enough to stand an R near my name.