Real Clear Politics has the polls on thirteen senate races where there is still some doubt about the outcome. Of the thirteen contests the Democratic candidate is ahead in five and very close in a couple of others. Where they are ahead they have a substantial lead. In three of the five races where the Democrat is leading, the Republican is the incumbent. The Republican senators most at risk are Dewine (OH), Santorum (PA), and Burns (MT). One race (MN) in which the Democrat is ahead the contest is for a seat vacated by another Democrat. One Democratic incumbent is trailing (Menendez, NJ), and one Democratic incumbent is leading (Cantwell, WA).
So, the upshot is that it appears that if the election were held today, and if these polls held up, the Republicans would lose a net two seats in the senate. A lot can change between now and November, however, and if the Republicans start campaigning on the issues Newt Gingrich lays out here, especially if they campaign hard on border security, they may be able to cut their net loss of seats to zero. Perhaps they'd even pick up a seat.