Here's my top 10 along with comments. Of course all of these are within the last few years because I've had GSN for...sheesh, just shy of 5 years now.
1) Russian Roulette - Best and well oiled machine GSN has ever created. Great game, set, host, announcer, music, drama, EVERYTHING!
2) Hollywood Showdown - Great Jackpot!-esque elements with Hollywood trivia and Todd Newton...should have lasted longer.
3) Lingo - Longest running original...what are we at over 200 some odd episodes in the can? Nothing like Chuck and his red balls, wait a minute...
4) World Series of Blackjack (The Vasgersian/Rubin seasons) - I'm a Vasgersian mark, sue me. I thought he and Max Rubin made a great hosting duo and made the action come alive, unlike John "just call me Ted McGinley" Fugelsang.
5) Whammy! - Season 2 was fine...Todd on Jolt cola we could have done without.
6) High Stakes Poker - AJ and Gabe get to me, but hey poker legends in one room betting their own bucks, not bad.
7) I've Got a Secret - Would have ranked higher except for the fact that Bil Dwyer, as much as I like him, still comes off like he's acting in the role of "stereotypical game show host" as opposed to actually being himself.
Ballbreakers - Underrated in my view. Fairly entertaining.
9) Cram - A bit cheesy, but Graham Elwood wasn't bad at all...and Icey, wherefore art thou Icey?!?
10) WinTuition - Not Marc Summers' best adult oriented game show. Decent enough idea, but some execution flaws were present.