Technically, the original Kamen Rider is the longest Rider series, but if you're only counting Heisei, then it might be.

Just looked into it a bit myself, the original Kamen Rider had a 98 episode run, not too shabby. For the Heisei riders 555 and Ryuki both are tied at 50 episodes a piece. With only 24 episodes, Amazon is the shortest series between both eras. Decade comes in just behind it at 31 episodes. Den-O and Agito are combined for the highest film count at 6 apiece.

Agito only had one film and a TV special.

What I get for going off of the Kamen Rider Wiki then eh?

Agito is 51 episodes and is the longest Heisei series at this point (Rider tends to get delayed due to sporting events both national and international so it tends to be around 48-49 episodes these days)
the original Kamen Rider ran for 98 episodes

EDIT: ack didn't see there was another page already. meh :P

The Kamen Rider wiki only lists 3 and note only one is a film. The others are noted as a TV special and Hyper Battle Video. No idea where you got 6.

Was going off the blurb on the right side of this page: http://kamenrider.wikia.com/wiki/Kamen_Rider_Agito

98 episodes is pretty substantial for a show, since there seems to be a magic cut off at 65 for syndication, if they even reach that point.

Anyway, 6 more episodes of Decade.
...I finally know what it feels like when someone doesn't finish that "99 Bottles of beer" song. Getting so far, but just ending without finishing.
The end goal is in sight. Less than an hour and a half worth of episodes to watch, but I just don't want to do it, especially knowing that ending, the ending that invalidates everything I just watched, will be coming up...
*Sighs* I suffered through so many episodes, and it's currently going 8/25 in terms of watchable/decent episodes...

Both of those numbers are wrong, in fact, those are Den-O's numbers. Scroll down to episode titles and special/movies. That's correct.

Agito is 51 episodes, 1 TV Special, 1 Movie, and 1 Hyber Battle Video.

Huh, well there I go making myself look quite the fool. Thanks for clearing that up for me.