Lots of great choices already. Here are some from me:
Rescue Terra I - VentureVision's sort-of prequel to Laser Gates (same programmer).
Shuttle Orbiter - Orbital mechanics and action puzzling? Sweet!
Tapper - Solid, fun, and wholesome (Mountain Dews for everyone!)
Subterranea - I so wish this game were more readily available; it deserves far more recognition IMO.
Bump 'N' Jump - It's a bit of a memorization game at its core, but besides that there's plenty of fun to be had here.
Room of Doom - A cool action shooter, probably my favorite CommaVid game.
Montezuma's Revenge - a better action/explorer game than Pitfall II. Yeah, I said it!