In no particular order:
Astros - It's not a retro baseball jersey thread without mentioning the "rainbow connection" of the late 1970s-1980s. But I also liked their late '90s unis when they closed out the Astrodome.
A's - Liked it when they wore the green tops in the Charlie O. days.
Braves - Loved the light blue road unis of the early 1980s. If I ever see a Dale Murphy throwback in that color, I'm buying it.
Pirates - Favorite road uniform of the "We Are Family" era was the black tops and gold pants.
Giants - The orange road tops from the early '80s.
Tigers - The road tops from the 80s-early '90s, when DETROIT was spelled out in capital letters.
Rangers - The 1974 unis, which they wore during a weekend home series last year with the A's.