I spent 2 hours doing some hardcore googling and came up with a nice list. I haven't been to most of these locations though, so any input or destinations no on the list is still appreciated
Putting my list here incase anybody else is interested.
AXIS Building (AXIS Gallery, Japan Industrial Designer's Association Design Museum, lots of ID related shops):
AXIS
Map here:
http://www.axisinc.co.jp/access.html
Droog Shop + Showroom:
Droog shop & show room
KDDI Designing Studio (keitais / cell phones):
http://www.kds.kddi.com/access/
Panasonic Center (Gallery, ECO/Universal/Math+Nature Design exhibitions, ECO house):
Access | Panasonic Center TOKYO | Panasonic Global
With the exception of Panasonic, which has exhibitions on the design process and concepts, seems like most big Japanese electronic companies have their showrooms oriented to shoppers.
JVC/Victor Showroom:
http://www.jvc-victor.co.jp/28s/
Sharp Ichigaya (Tech + History showrooms):
http://www.sharp.co.jp/corporate/showroom/index.html
Sony Building:
Sony Building -English site-