Wolski, a forward, is the significant piece of this deal, adding to a Coyotes lineup that is starved for offense.
Wolski has 17 goals and 30 assists this season, but had fallen out of favor with the Avs. Wolski, the 21st overall pick in 2004, immediately will become a top-six forward for the Coyotes.
"Wojtek Wolski is a terrific young offensive player," Coyotes general manager Don Maloney in a statement. "He is a talented goal scorer that will help us offensively and on the power play. He has great size and is just entering the prime of his career."
It is Stempniak's third team in five seasons; he will be an unrestricted free agent on July 1.
Mueller, the eighth overall pick in 2006, had a terrific rookie season with 22 goals, but his production has fallen off the past two years and he has been inconsistent. The 21-year-old has played in 54 games for Phoenix this season, but has only four goals and 13 assists.
Porter -- who, like Mueller, is a forward -- played at Michigan, winning the Hobey Baker as the top collegiate player in 2007-08.
Porter, 23, was a fifth-round selection in the 2004 draft, and made his NHL debut with the Coyotes last season, with five goals and five assists in 34 games. He has spent most of his time this season with the San Antonio Rampage in the AHL, recording 15 goals and 25 assists in 52 games.
"These two players fit into our philosophy and they both have the best years of their professional careers ahead of them," Avalanche general manager Greg Sherman said in a statement.
Information from ESPN.com's Scott Burnside was used in this report.