Foam rollers

[OakLeaf]

Most sporting goods stores have them; any physical therapy clinic or athlete-oriented medical supply place will.

As far as how and when to use them ... that's a huge question. Two broad categories - self-myofascial release (both therapeutic and preventive), and advanced balance training. I don't have a link handy to good videos, but there's a lot on YouTube.

I suppose you don't really need to know much to get started on SMR. Roll around on it. Don't roll directly over a joint. Give extra attention to sore spots and knots, and expect it to hurt some, but don't go so hard that you tense up trying to unweight the area, or so long that you're excessively sore afterward. I just read something (sorry I don't have a link) that said unlike static stretching, foam rolling before exercise can be beneficial - but most people will do it after their workout as a preparation to stretching.