What's the easiest way to measure...

[toaster]

...head tube and seat tube angles off a bicycle?

Maybe a protractor and a contractors level?

[dave thompson]

Hardware stores, including Ace, Loews and Home Depot, sell relatively inexpensive angle finders that you hold to the appropriate tube and will tell you the angle, assuming that bike is on its' wheels and on level ground. Some of these angle finders are magnetic and work well with steel frames.

[happycampyer]

Also, if you have an iPhone, you can get a clinometer app for $1. Not necessarily as precise as a dedicated clinometer, but it can be handy.

[Louis]

A while back I bought one of these from the linked site. Works like a champ, even after having dropped it on the floor once or twice.

Wixey Digital Angle Gauge $28 (http://www.craftsmanstudio.com/html_p/C019003.htm)

http://www.craftsmanstudio.com/images_p/C019003.jpg

[Dekonick]

Hardware stores, including Ace, Loews and Home Depot, sell relatively inexpensive angle finders that you hold to the appropriate tube and will tell you the angle, assuming that bike is on its' wheels and on level ground. Some of these angle finders are magnetic and work well with steel frames.

+1 - I have one and it is quite useful.