(I know last week I talked about December, 1980; I don't think I actually bought anything that was on sale in January, 1981, at least not when it came out.)
Marvel Premiere 58 featuring Doctor Who. If memory serves, I still wasn't able to watch Doctor Who on TV at home, so these comics felt even closer to watching the show than reading the novelizations of the TV series. The stories, by Pat Mills and John Wagner (whose work I'd later come to love in the pages of 2000AD did a great job of combining the weirdness and humor of the series with larger-scale adventures (in four page weekly installments), and the art, by Dave Gibbons, was gorgeous. And the cover was by Frank Miller and Terry Austin!
And again, if memory serves, my purchasing this comic was the result of my calling the store every week to find out if it was out yet. And when it did come out, I either convinced my mom to drive me down to Telegraph Avenue, or convinced my dad to pick it up at the store after work. So thanks again, mom and dad, for helping me find this thing that I love.