"Pennsylvania (Santorum-R) - I'd say Sen. Rick "Man on Dog" Santorum is probably going to be in trouble in this Democrat-leaning state. This, along with Montana, might be their best opportunity for Democrats to strong-arm a Republican incumbent out of office and cut the GOP majority in the senate. Possible Democratic opponent is former state Treasurer Barbara Hafer, state EPA director Kathleen McGinty or 2004 senate nominee former Rep. Joe Hoeffel.
Tennessee (Frist-R) - Senate Majority Leader Frist vowed to only serve two terms in the senate, so may not run for re-election and may instead run for president in 2008. If Frist doesn't run for re-election, Rep. Harold Ford (D) and Rep. Zack Wamp (R), who has already begun to raise money for his senate bid, will be top contenders to replace him. Another distinct possibility exists: Frist may be named Vice President in the next two years if Dick Cheney's health takes a turn for the worse.
Montana (Burns-R) - Born Jan. 1, 1935, Burns will be almost 72 on election day in 2006. Burns won a tight race (51% to 47%) in 2000 over Brian Schweitzer (D), who was elected governor in 2004. Aside from taking the governor's race in 2004, Montana Democrats took control of the state senate and state house and now hold most statewide offices. Dems will try to capitalize on this momentum in 2006 by making a serious challenge against Burns. One possible candidate is Attorney General Mike McGrath (D).
Rhode Island (Chafee-R) - Like Sen. Snowe, Chafee is likely going to be a target of ultra-conservatives groups like the Club for Growth. Chafee has flirted with the idea of switching parties, which he may yet do if the Democrats retake the senate in 2006. The Dems had better find a strong candidate, just in case. Rep. Patrick Kennedy (D), son of Sen. Ted Kennedy (D-Mass.), has decided not to make a bid for the seat. Possible Democratic candidates include Secretary of State Matt Brown, Rep. Jim Langevin, former Lt. Gov. Richard Licht, former Rep. Bob Weygand and former Attorney General Sheldon Whitehouse.
Mississippi (Lott-R) - Lott could face a strong opponent who might take advantage of Lott's public depantsing over remarks that some believe were racist. Possible Democratic challengers include former Attorney General Mike Moore.
Arizona (Kyl-R) - Jon Kyl will be 64 in election year and will likely run again. Arizona Democrats may go after Kyl, hoping to make inroads in this swing state. A possible opponent is state Democratic Chair Jim Pederson.
Indiana (Lugar-R) - Lugar is safe if he runs again. He was born April 4, 1932, and will be 74 in election year. If he retires, there's a pretty good chance the GOP will hold the seat."
http://www.modernvertebrate.com/elections/2006-national/