"Historic" toku Doesn't every toku fan eventually feel the lure of the King of the Monsters? And the one constant for that series is the original movie - Godzilla.
The original TV toku trilogy - Ultra Q, Ultraman and Ultra Seven. We wouldn't have henshin heroes without them. Although I'd suggest actually watching them in the order Ultraman, Ultra Seven then finally Ultra Q.
Movies Mechanical Violator Hakaider - stylish albeit weird film that I kinda prefer over the two 70s Kikaider series.
Gamera 90s Trilogy - IMO the third film kinda runs out of steam, but many love it and consider it one of the great toku trilogies.
Negadon: The Monster From Mars - half hour animated tribute to the old Toho monster movies, and pretty interesting in it's own right.
Death Game Park - Shinken Red kicking ass in a 'battle royale' style situation (originally released on cellphones(!) as a series of shorts but can be watched as one big movie)
Series Tekkōki Mikazuki - mecha mini-series that shows a lot of the style that would later go into the Garo series.
Chō Ninja Tai Inazuma! - two 45 minute episodes in which the main cast of Magiranger, assisted by actors from Dekaranger and Boukenger, both pay tribute and mildly parody Sentai.
Ultraman Mebius - the show that sold me on the Ultraman franchise and still the one I like the most. And it's available for free!
Keitai Sousakan 7 (aka Cellphone Investigator 7) - a tentative inclusion from me, as I happen to be watching it at the moment and I'm only a dozen episodes in. :sweat: No monsters or transforming heroes, but it's got a bunch of familiar faces in it (Kamen Rider Knight, Kamen Rider L'Arc, Hurricane Blue...). As a change from the norm I'm enjoying it, and it has a pretty good reputation.
Spiderman (the Japanese version)
I'd love to check this out just for the sake of curiosity, but it's pages on the Marvel site have the actual videos on youtube...and they've been blocked as copyright violations <facepalm>