(Via Krikorian), NumbersUSA has some lists of where various senators stand on the DREAM Act. The following have committed to voting against the measure:

Alabama: Sessions; Shelby [Update]
Arizona: Kyl
Georgia: Chambliss; Isakson
Kansas: Roberts
Kentucky: Bunning; McConnell
Louisiana: Vitter
Mississippi: Lott
North Carolina: Burr; Dole
Oklahoma: Inhofe
South Carolina: DeMint; Graham
Tennesee: Alexander; Corker
Wyoming: Enzi

That's 17 votes. [UPDATE: 18 votes with Shelby] "Grand bargainer" Graham is against this measure, and Sen. Martinez, who isn't included above, sounds skeptical about it being attached to a defense bill.
It also has a list of those who are not committed to voting against the DREAM Act (though some on this list have declared that they will vote in favor of it--e.g. Durbin).
UPDATE: NumbersUSA has added Shelby (R-SC) to the confirmed "No" list. (H/T a reader)