The team announced the deals on Tuesday. Lewis and Stanback played their college ball at Washington.
Lewis was a special teams standout for the Seahawks, but he also saw significant time in the secondary. Lewis played in 14 games and ended the season with 17 tackles and one sack. He also had eight special teams tackles. Lewis missed the final two games of the season after suffering a knee injury.
Stanback missed the entire 2010 season after rupturing his Achilles' tendon in training camp. The Seahawks were high on Stanback's prospects before his injury.
In addition, the Seahawks announced Wednesday that they signed running back Chris Henry for the 2011 season. Seattle spent last season on Seattle's practice squad before being placed on injured reserve in January with a foot injury.
The Associated Press contributed to this report