Florida: This will likely be one of the first 2016 Senate races to begin to shape up. It already appears that Debbie Wasserman Schultz has fizzled out and likely wont even seek the seat. The other Dems that are likely to run are Patrick Murphy (who is right now the strongest and most likely candidate), Alan Grayson, and Charlie Christ. Though Christ is the least likely of the three. The biggest question is whether Marco Rubio will run for reelection for the GOP or if he will run for the Presidential nomination. He has stated that he will not seek both offices at the same time. Florida is likely the Democrats 4th best shot at a pickup in 2016. Without Rubio in the race, this could be a very winnable race should the right Democrat jump in.
Georgia: Johnny Isackson will be 71, but will be running for another term. This will be an extremely difficult seat for the Democratic party to flip. Possible contenders include Michelle Nunn and Jason Carter. While both of them could make this race a long shot, it is still not likely. That being said, who knows if anyone will challenge Isackson in the primary. An open seat, in 2016, with a Nunn or a Carter could make this very competitive.
Hawaii: Brian Schatz won his special election in 2014 for this seat by over 42%. This might be one of the safest seats of this cycle. The only thing that would make this a race would be in the primary if Colleen Hanabusa decides to challenge Schatz again in the primary.
Idaho: This one is in the same boat as Hawaii. Even more safe in that Crapo will dodge having Rep. Raul Labrador as a primary challenger. Outside of 2014 Gubernatorial nominee A.J. Balukoff, there is essentially no Democrat with the Statewide profile that could run. Crapo won this seat in 2010 by 46%, ran uncontested in 2004, and won by 42 in 1998.