This is the current baseline model based on the polls collected over at pollster.com (including those by Mason-Dixon, PPP, and Rasmussen). Subsequent projections will incorporate the latest polling results.
Currently the balance of power in the Senate is 59 Democrats (57 Democrats plus 2 Independents that caucus with them) versus 41 Republicans.
I currently project that the seats vacated by Dorgan and (originally) Biden will go strongly to the GOP.
I also project that Nevada is a very likely GOP pickup, beyond just from polling we have the general consensus that Senate Majority Leader Harry Reid is in extremely deep trouble in Nevada and is likely to be Daschled. Bennett, Lincoln and Specter have seen their approval numbers crash thanks to their votes on Health Care and the Stimulus Package, and their head-to-head polling against various GOP contenders make these BARELY Republican pickups.
Total gain by Republicans of 6 seats.
The seat in Missouri is being vacated by the Republican incumbent Kit Bond and is hotly contested between Blunt and Carnahan. Illinois in polling has gone back and forth (being vacated by the Democrat) and with multiple contenders from both parties will be difficult to nail down until after the primaries.
Good news currently for the Republicans.