I have a neat trick of photographing people without them knowing I'm taking their picture. Usually I take a shot of them and then immediately look beyond them as if I'm taking a picture something behind them. Then I pretend to study the settings on the camera. This gives me another chance to shoot, while they stare directly at the camera. Some of them get confused.
The trick here is not to look directly at the subject. You can stare at them for as long as you want from behind the viewfinder. Some are courteous and try to walk out of the frame. In that case just keep clicking. With a wide lens you can achieve anything. :)
This is how I took this one. This guy was walking down like a tiger and I had to get a shot of him. Tattoo and all. Its a pity I can't use the coloured version of this picture (you can't see his face properly in colour). He's wearing yellow and blue shorts and has a tattoo on his left forearm. I'll try putting up the other picture also.