Right now only two games come to my mind, that were likely pretty popular when they came out but no one has likely heard of, or played much since..
Zedblade, for Neo Geo.
Stargunner, for IBM PC / MS-DOS.
Both are excellent side scrollers with great visuals and excellent music.
Also I just thought about another game for MS-DOS. Knights of Xentar (Dragon Knight III in Japan). I first came across KoX on AOL when I was 13 or 14, somewhere around that age.. I know not many people played it for sure, as it was an Adult Hentai RPG. Though it came as a roughly 14/15MB compressed zip, it was a R.I.P without the CD and lacked the actors spoken dialogue. Which it turns out is a good thing because it is horrible (I have copies of both the RIP version and the CD version).. BUT it was still fun to play as an RPG. It had some unique combat mechanics among other things and played just like a console-style RPG for the most part only you used your keyboard and/or mouse.. The music was sparse in selection but it had a few memorable tunes as well.. Including the generic getting laid music that played when you slept with girls.. It had that cheesey porno feel to it that makes you want to giggle