Terms of both deals were not disclosed.
Miller, a 10-year veteran, is the second former Chicago Bears quarterback to sign with the Bucs this offseason. The team inked QB Shane Matthews to a one-year deal earlier this month. Miller and Matthews were teammates in Chicago from 1999-2001.
Chicago released Miller for salary cap reasons after the 2002 season concluded. Miller, who's been plagued by the injury bug in recent years, underwent shoulder surgery this offseason to repair a torn rotator cuff and he won't likely be able to throw at full strength until June or July.
"We're excited to add Jim Miller to the mix," said Bucs head coach Jon Gruden. "Our goal is to get him healthy and teach him our system. He is a proven playmaker and leader."
Miller, 32, said Tampa Bay was first on his wish list in terms of teams he'd like to play for.
"I'm excited to play for the World Champions," Miller said. "They have given me a great opportunity to come down here and play. I want to be healthy for them and help in any capacity that I can. As for working with Jon Gruden, you know it's funny, I made a list this offseason of what coaches I wanted to play for with great offensive minds and he was the first one on my list."
Miller played the past five seasons with Chicago and he led the Bears to the NFC Central Division title in 2001. Miller has thrown for 6,387 yards and 36 touchdowns and 31 interceptions during his career. Miller entered the NFL out of Michigan State in 1994 as a sixth round draft pick of the Pittsburgh Steelers.
Oben had been one of Tampa Bay's top priorities in terms of re-signing players this offseason, but limited salary cap room kept the eight-year veteran left tackle out on the free agent market a bit longer than both sides would have preferred.
"I feel good about how everything turned out," Oben said. "It is great to re-sign with the Buccaneers and I look forward to helping us start off like we finished last season and it helps by having the same guys line up together again. Now that it is completed, I can concentrate on playing football and getting more acclimated to the community."
After signing a one-year contract with the Bucs last year, Oben started all 16 regular season games and all three post-season contests last season. Oben was part of the Bucs offensive line that only allowed one sack during the team's two playoffs games and in Super Bowl XXXVII.
"We're proud to have Roman back in the fold," said Gruden. "He is a key member of last year's football team and we feel will he will be a key member of this year's team."
Oben has started 93 of the 98 games he's played in since entering the NFL out of Louisville in 1996 as a third round draft pick of the New York Giants.