If you go for a cooler with push pins, don't get one that is heavy. Push pin design is fine if the cooler is not too heavy. I have seen some huge coolers use push pins, and it baffles me why the makers did not use a more substantial mounting method. I have never liked the push pin idea, it's fine if the cooler has a sprung bracket which can take the tension, and is also light.
Push pin coolers might be somewhat easy to fit, assuming they have a tension bracket. But like I discovered, solid frame coolers, like the ones that come with Intels cheaper range CPU's, are crap. I Built a PC for a friend 4 months ago, he got a E5200, great CPU, crap cooler design. Due to the solid plastic frame, there is no spring that allows the cooler to be tight on the CPU, but also not so tight it bends the board. Due to the solid frame the pins are attatched to, the board bends instead, far more than is healthy imo. So much so, the 4th pin would not clip in place. I ended up fitting the cooler that came with my E6300, which is a far better design, as it has a sprung metal bracket that flexes when the clips are pressed down, allowing it to be tight, but it doesn't bend the board. Obviously, Intel saving some money on their cheaper range by including crap coolers. Recently bought a E5200 for a media PC I'm building, so of course ran into the same problem. Intel should be slapped for providing such rubbish with their cheaper CPU's.
If you rule out any cooler that requires the board to be removed, you are ruling out a lot of the best ones. Of course, the ones that require back plates etc, are generally bigger. Bigger = more money usually. Arctic Cooling's Freezer Pro 7 is a good choice, it uses push pins, so it's easy to fit, but isn't too heavy. Also it's very reasonably priced. Like Butler said, probably the best bang for buck cooler there is. If you go with that, make sure you get the Pro 7, they do a Freezer 64, but that's for AMD CPU's.