Used Miles Converted, Now What?

I have around 8,000 miles/points in United, Marriott, and other various places. I saw where most you have the ability to eshop and earn for that particular program (most converts from each program need 10,000 as a minimum) to gain enough miles/points to do the swap according to the mileage converter page. If tells you how each thing is converted into other programs to eventually get to where you want them to go, but where is there a place to do that? I've heard of points.com but I'm not to familiar with them and it cost $ to join. Was wondering if this is the site that allows me to move the miles/points and was actually worth the money or if there were other websites out there?