I've always, for some reason, had a liking for Gun Riders. Eithers its the character or the design but interestingly enough I don't like the Gun as a weapon that much (well atleast for Rider).
I liked Zolda as well as Kitaoka (the character), he's one of the many great (and possibly my favourite) characters in Ryuki and there's tons of them. I miss the Rider shows where there are a different array of Riders and most of which had some good amount of development, Ryuki being one of the best shows to do it.
In terms of gun riders, I also like RoboRider, Hikawa/G3, Kaixa (if you consider him the gun rider), Garren, Ibuki and Drake. None of the recent ones though, both the kiddy Ryuutaros and Bassher weren't appealing to me.