I don't know about everyone else but I bought a pair of 5.11 taclite pro pants for $55 that have knee pad pockets and they seem pretty nice. I haven't had a chance to put them through the paces yet though.
I no longer use 5.11 pants because I find they bind in the seat and knees. I have used TruSpec pants with the TruSpec pads with good results. Also used the same pads in the knee pad pockets on Eotac pants. Eotac is out of production.
Your probably looking at the Crye Precision combat pants, I own a pair and they are nice...but expensive. Another nice pant that is new to the US market it this: http://www.repconnw.com/index.php?page=s...&Itemid=109
These are a little more affordable and the drop in knee pads are nice! Alot of 3-gunners are using these, including myself.
I use woolrich elite. They have pockets for the knee pad inserts. The problem with the knee pad inserts is sometimes they aren't centered on your knee when you kneel down. It is painfull to say the least. The pants material in the area of your knees will quickly suffer abrasion & start to rip/tear since the pads are on the inside of your pants. I started using arc teryx knee pads & solved both problems. Just something to think about before you ruin a set of pants.