Soul Gambler is pretty good. Rather short but still interesting.

You could try Higurashi When They Cry, but I must warn you that it's a psychological horror VN and it's pretty dark.
If you like the cyberpunk setting here's another good one: VA-11 HALL-A: Cyberpunk Bartender Action
Oh, yeah, you should also play To the Moon, but I think you already did it, if not, what are you waiting for?

Alternatively to the post above, you could buy Higurashi straight from MangaGamer and DRM-free according to information I received about it, just in case you don't mind not buying it on sale for the DRM-free advantage. While it is very graphic, it has a memorable cast with personalities to care about and an intriguing setting.

If you want some pointless comedy to kill your time with along with a couple of fanservice/ecchi/hentai, you could get the newly emerging Sakura games.

Not quite a graphic novel but Wolf Among Us and Back to the Future are great stories with a few puzzles and plenty of interraction. If you them I have spare keys I'll trade against cheaper Steam games on my wishlist as I haven't managed to trade either for some reason. Look them up.

Also I recommend The Detail (don't have a key for this).

I recently really enjoyed the character of Hector Badge of Carnage (telltale). More puzzles in this game but nothing too taxing and a genuine hilarious dialogue.

If you still have money after all the good recommendations, check out The Silver Case
Odd that no one has mentioned this :)

Yet more +1 for Steins;Gate , Clannad and The House In Fata Morgana

And good for last day checking at reddit Visual Novels in the Steam Winter Sale (+Announcement)