The first is from June 1979 (issue 169) and is the earliest I could find (and - I think - the first published). The top five make for interesting reading and really capture the STARLOGGED vibe. The X-Men and Spider-man are there (of course) but so are The Micronauts (1), Star Wars (2) and and the 4th issue of Battlestar Galactica (4). Hurrah.
By way of a comparison, the second Top 100 is from February 1981 (issue 188) shows that the 23rd - and final - issue of BATTLESTAR had plummeted to 32nd place. No wonder Marvel decided to cut their losses once the TV show bowed-out (save for GALACTICA 1980 and the syndicated cut-and-shunt teleflicks) back in the summer of '79. The 'nauts and Star Wars (now joined by Star Trek and Rom) were - in comparison - faring much better. Also lurking - towards the bottom - of the 1981 chart are the likes of Buck Rogers (73) and Battle Of the Planets (75) amongst a bunch of other books for younger readers which must have had limited appeal to comic store patrons.
It's worth noting that these charts were compiled in a different way than similar charts you see today. The sample is based on a small number of comic book stores at a time when the bulk of sales were still via traditional (although declining) outlets. We were still a little way away from the first Direct Sales comic (Marvel's DAZZLER issue 1, 1981) and the wholesale shift in sales over the first part of the eighties. These charts were also based on actually sales rather than retailer pre-orders from their distributor. As such, they give a more honest picture of what was really selling as opposed to what retailers anticipated selling.