Frist, of course, is retiring (for a putative Presidential run in 2008), so his seat is open. Tennesse is a pretty reliably Republican State these days, but Ford is a Democrat I've been watching for a while and he'll be tough to beat should be become the Democratic nominee:

NASHVILLE, Tenn. Democratic Rep. Harold Ford Jr. filed the federal paperwork Wednesday to run for the Senate seat being vacated by Republican Majority Leader Bill Frist.

The five-term congressman from Memphis is the second Democrat to enter the 2006 race. Frist has said he does not plan to seek a third term.

"I'm excited. I'm ready to go," Ford said in telephone interview from Washington. He said his top issues will be energy reform, national security and education.

Telegenic, intelligent and well-spoken, Harold Ford is the Democrats dream Senatorial candidate in Tennessee...and being black isn't going to exactly hurt his chances for (a) massive black turnout and (b) 95%+ of the black vote going Democratic; two things ever more necessary for a Democratic victory in the south, especially in State-wide races. The scion of a long-standing Tennessee political dynasty, Ford is connected to all of the State's power brokers and will not lack for anything in the general election. Additionally, Ford will have cross-over appeal as he has at times bucked the far-left leadership of his Party, including challenging Pelosi for the Minority Leader post after Gephardt stepped down.

The GOP will need a really good candidate to beat Mr. Ford. If I sound grim about this, then that is intentional...we've really got our hands full in Tennessee if Ford is the nominee.

UPDATE: Maybe not...