A nice take on the transparent billboard variety: "Constructed from semi-transparent resin, the billboards accurately blur the scene behind them regardless of day, weather, or season."
-- Ian Hart
Transparent Billboard for DIY Stamps in Estonia
Transparent Billboards for Amnesty International
Transparent Billboard by Nike
A very smart way to take advantage of a typical behavior: place a realistic-looking cut-out of a police car to slow the drivers down and read your billboard. This billboard for a Turkish bank reads, "Pay your traffic tickets on time without waiting in line - isbank.com.tr".
-- Frederik Samuel
Two brilliant ideas for anti-dandruff shampoos. The billboard has little transparent notes that you yourself remove from the hair. The photobooth tricks you into taking a photo of your scalp. Simply brilliant.
An installation in China to promote a tennis competition consists of a giant racket with trampoline functionality and a guy jumping up and down. The copy reads:
"The fastest server generate over 560 Newtons. Enough force to propel a human skywards.
Experience the best tennis at the tennis masters cup 2006".
-- via Ads of the World
Ice sculptures shaped like pregnant moms with a plastic baby inside where installed on the streets to melt. The point? "Over 30 million children lose their moms to tobacco every day." More at Trend Hunter.
keywords: billboard, outdoor, guerrilla
Actually, I'm not sure it's Tokyo, but it's definitely from Japan and it promotes Nintendo DS. It comes from Plastic Bamboo.