If you're ok with unfinished games, I actually prefer these to most of COG's published titles:
Blood For Poppies
A Jinni of the Seven Winds
When In Rome
Vendetta: Rise of a Gangster
Team Zero
Otherwise, I guess I'd just recommend trying out all of the free games on the COG website if you haven't already. As for COGs that aren't free, I'm not sure which you've played, but I'd especially recommend (in this order): Choice of Robots, Tin Star, Slammed!, Zombie Exodus, Sabres of Infinity, Mecha Ace, Paradox Factor, Life of a Mobster, Choice of Kung Fu, Choice of the Star Captain and The Heroes Rise Trilogy.