Don Wakamatsu, Geren's bench coach last season, was named Mariners manager last month and promptly hired Ty Van Burkleo, Oakland's hitting coach from 2007-08, as his bench coach.
Waller, 51, joined the A's coaching staff in 2007 as first-base coach and split his coaching duties last year between first base and third base.
"One of the things I love about Tye is what a positive, upbeat personality he has," said Geren, who has known Waller for more than 25 years. "He and I think a lot alike, but he's not afraid to give his input if he's thinking something different than I am in a given situation, and that's important.
"He's also an excellent communicator, and he's someone I have a lot of faith and trust in."
Skaalen, 54, joins the A's after spending the past two seasons as Brewers hitting coach. In his first season on a big league coaching staff, in 2007, Milwaukee hit a franchise-record and MLB-leading 231 home runs.
Skaalen began his coaching career in 1981 at Class A Daytona Beach and managed in the Minors for the San Diego (1982-86) and Texas (1987-89) organizations. Skaalen also has served as Minor League hitting instructor for Texas (1990), coordinator of Minor League instruction for Seattle (1991-96), director of player development for the Padres (1997-99) and Minor League hitting coordinator for the Brewers (2000-06).
Skaalen played professionally for three seasons in the Baltimore organization and batted .246 with 15 homers and 123 RBIs in 251 games.
"Jim's a San Diego guy, too, and I've known him for at least 20 years," Geren said. "He's also someone I have a lot of respect for, and his track record as a hitting coach speaks for itself."
Steverson, 37, spent the past four seasons managing in the A's farm system, most recently at Triple-A Sacramento, where he guided the River Cats to their second consecutive Triple-A and Pacific Coast League championships in 2008.
Steverson has a career record of 297-264 as a Minor League manager, including stops at Class A Stockton in 2005 and 2006, and Double-A Midland in 2007. Steverson joined the A's organization as hitting coach for Class A Vancouver in 2004 after spending five seasons coaching in the St. Louis farm system from 1999-2003. He played professionally for seven seasons, including in 31 Major League games with Detroit (1995) and San Diego (1996).
"Todd has been with the organization for a while now and had success wherever he's been, so he really knows how we do things," Geren said. "He's going to be working with a lot of guys he already knows, and that's going to make the transition that much smoother."
In a press release, the River Cats announced that they aren't expecting to name a replacement for Steverson until January.