Dave,
I got a new pair of 661 Kyle Strait kneepads a few weeks ago after having a few spills whilst wearing only a pair of Federal ACL Knee Gaskets (neoprene) and would highly recommend them. They were recommended to me by Alan @ Alansbmx.com, and after a spill whilst riding a spine ramp last night, I gotta say they've already more than made it worthwhile buying them.
They're just about wearable under jeans (baggy jeans, none of these skinny fit, girls jeans...) and I wear them with a set of MPS shinpads.
I also use 661 chicken wing elbow pads, but they kinda spend most of their time in my bag...
Brian
ps, and i wear odyssey 3rd base gloves too.