I have the AlpineStars Boinic Knee Guards and they are very good.
http://www.alpinestars.com/Bionic_MX.../p/650633.html
They tend to slip a bit while walking (i wear them a wee bit loose) but on the bike, they are very comfy and have a robust sturdy feel.
@VK - go with Icon. They are pretty good too. If these carry CE approval / certification, much better.