you can use the "Snap to Curve" to do exactly what you're after. Select your object/vertex then hold down the "C" key, and middle mouse drag your vertex to your edge.
Also if you want to place a vertex you can use the split polygon tool and place it where you need it then press enter.
2 x Modeling Challenge Winner
Last edited by jsprogg; 18-05-2014 at 10:07 PM.