Roy, 29, struggled to recapture previous form in 2011-12 after suffering quad and hamstring injuries over the previous 12 months. The centre finished with 17 goals and 44 points the past season, down significantly from a four-year stretch beginning in 2007 in which he averaged 26 goals and 70 points per season.
"Derek Roy is a legitimate top two line centre, and has been productive throughout his career," Stars general manager Joe Nieuwendyk said in a statement. "He is a proven commodity that helps fill a void at a position of need for our club. We believe Derek helps make our hockey club better and we are happy to have him."
Ott, who turns 30 next month, finished with 11 goals and 28 assists in 74 games. The gritty forward from Summerside, P.E.I. has scored 85 goals and 135 assists in 566 NHL games, with 1,170 penalty minutes.
Pardy, 28, finished with three assists and 16 penalty minutes in 36 games with the Stars last season. The six-foot-four Bonavista, N.L., native has scored four goals and 25 assists in 183 NHL games, with 157 penalty minutes.
With the addition also of enforcer John Scott on Sunday, Sabres general manager Darcy Regier has clearly made strides to toughen up his club.
Roy earns $5.5 million US in the final year of his current deal in 2012-13 with a salary cap hit of $4 million.
Ott represents a $2.95 million cap hit over the next two seasons. Pardy's cap hit is $2 million for each of the next two seasons.