There was this $180-$200 monstrosity back in the early PSP era: The PSP2TV: Never knew that the GBA had a TV Tuner until recently:
I have both of those... Datel also made a double-capacity battery for the PSP that looked about the same as the 4gb hard drive. So if you had them both, each side of the PSP had a huge thing stuck to the back of it... And the PSP2TV also came with a replacement faceplate and flex circuit board you had to install that added a large connector for the TV out and the joystick connector... It was an interesting solution to the TV out problem on the early models..
not really an accessory, but the panasonic gamecube surprised me. not sure what the point of it was but its p strange.
Wondered how long it would be before someone posted the Rez vibrator. I've seen a couple pop up for sale and nearly bought it, just for the novelty value. But the idea of displaying a second hand dildo always makes me change my mind
4Gb HDD for PSP? What was the point? I got my first PSP in 2006 and 2Gb memory sticks were already available. 2-3 years later Micro SD to MS Pro DUO adapters arrived and solved all problems . Haha, so true!
Still the only Nintendo console that play DVDs... I'm still surprised by that fact. First thing I did with my Wii U is to try a DVD, what a disappointment.
I have one of those, not the tenga the novint falcon. It's pretty cool and only works for a few games though.
Price if I remember correctly. I think the 4gb hdd was cheaper than a 2 gb Memory stick (or it was definitely cheaper than a 4gb one). And it was basically a compact flash adapter, so you could put a 16 or 32 GB compact flash card/drive in it if you wanted to...
I had this, was not something I used as I could never get into the game. I'm pretty bummed that somehow I got rid though.
There is that N64 Bio Sensor Used with Tetris64. https://en.wikipedia.org/wiki/Tetris_64 It checks your heart rate, that changes your gameplay.
I wanted to import it back in the day to try out the sensor. Apparently it reacts to your heart rate to speed up the game. A lot of reviewers said it sorta worked but not quite fully.