Here are my favorite cards for the Astros released in 1981:
J.R. Richard Donruss #140
Nolan Ryan Kellogg's 3-D Superstars #6
Frank LaCorte Donruss #143
Joe Niekro Fleer #54 - just love the "you talkin' to me?" expression on his face.
Joe Morgan Topps #560
Joe Morgan Fleer Star Stickers #109
Nolan Ryan Donruss #260 - a slightly different Nolan card - he's usually shown starting his leg kick instead of driving towards home plate.
Jeff Leonard Topps #469 - Moustache.
Don Sutton Topps Traded #839 - yeah, that's right, Topps Traded in 1981 was a super high numbered extension. Next year, they number the traded set separately with a T at the end.