i have the zalman 9500 and i love it. i have made countless posts on CF praising it which should give an idea of how good of a product it is.
it keeps my CPU frosty which is the main thing i like about it obviously, but where it really stands out from the others is its simplicity and effectiveness in installation. it doesn't use those stupid pushpins like a lot of other LGA775 HSF do. the motherboard has to be removed to install it, which is the only negative thing about it that i can possibly think of, but most of us on here can remove and reinstall a motherboard with our eyes closed so its no big deal.
you mount a bracket onto the back of your motherboard and then screw the base of the HSF onto the bracket. once that is done, you use a retention clip to hold the fan and heatsink in place. it is all amazingly simple and easy to do, and effective too. once the heatsink is on, you KNOW it is on correctly and you don't have to wonder if it is on 100%, or if it will come loose like you do with the pushpin method. if you need to remove the heatsink for any reason you just push down on a clip and it pops right out.
my temps have been lower than i have ever had them before with any CPU, and this is using the 9500. the 9700 for a little more money is even more effective, and uses the same installation that i love so much. all in all definitely worth your money.