Foam Rollers are great tools for self-massage, a warm up tool, and an effective way to stretch muscles.  They can help increase range of motion/flexibility and are great for helping to decrease inflammation, tight muscles, and pain.  They typically come in 12, 18, 24, and 36 inches.  I like the 24 inch one as it's easy to use and store.  I use it before and after workouts or when I have a pesky tight muscle.