Plantronics provide the best no nonsense bang for the buck, I've had the same pair for close to six years now. Replaced them numerous times for the "latest and greatest" but always end up pulling them back out of retirement.
spl= sound pressure level. Over the ear hp would tend to put out more spl than on the ear type due to design. I perfer over the ear myself.
Pick your poison:
http://www.plantronics.com/north_america/en_US/products/cat640035/cat1430032 Beware of usb based headsets and vista. Plantronics havent updated some of their drivers lately.