In chronological order:
Turbo Brace. I love how when they press the button the turbocharger runs.
Dino Buckler: Still one of the most unique devices around. And funny how the same year Kamen Rider had a no-belts policy. :lolol
Power Brace: I just love the mechanism.
Digitizer: Cool-looking device with the keypads and I love how certain codes do things.
G-phone: While Keitaizer was the first phone this made it the norm.
SP License: It's what if the swiss army knife was a morpher. :lolol
Magi Phone: Loved how it became a wand, matched the whole magic theme.
Accellular: Very rigid and tactical look got me hooked at the time.
Shodo Phone: The brush gimmick was on point.
Zyuoh Changer: Real good use of the cube aesthetic.

I don't know why but I really love LuPat's changer.