An AtlasNova Green Laser Pointer. Availible for under $80, IIRC, there may be a deal on either the power, or the price, if you give them your CPF username. Someone fill in if they know the details of any current deals...
This is what you want without a doubt.
The green beam is visible from the SIDE, at night and in dark rooms. A 5mW green laser is approximately 20x (twenty times) brighter to the human eye than a red laser of the exact same power.
http://www.abeland1.com/
I don't know your location, but beware of certain sellers who sell this or similar pointers modified to over 5mW, they may not be legal to import to your country. For instance, lasers over 5mW are not legal to import into the US without safety devices like a key switch, shutter, "deadman" switch plug, and a lens shutter.
Remember when "impressing your friends" don't do anything dumb, namely anything in the big red warning paragraph that sits atop this forum.
Green lasers have gotten some bad press in the past year, and are subject to some sensationalizing that can and has caused scrutiny and regulation that unfairly impacts legitimate and responsible users.