The Democrats currently hold 55 seats. Two seats are held by Independents (Bernie Sanders - VT & Joe Lieberman - CT) who will likely caucus with the Democrats - although on defense issues, Lieberman is at odds with the Democrat Party. The Republicans are currently sitting at 40 seats with 3 left to decide. The last three seats are of critical importance if the GOP is to have any say at all in the direction of this nation. If the Democrats gain control of 60 seats, Republicans will be unable to filibuster even the worst legislation (and more importantly judicial nominations) proposed by our entirely Democrat government.
In an effort to keep this in readable chunks, I'll cover each race in readable chunks.