Jump Rope!

If you don't jump rope, you need to.  Look around, any legit athlete jumps rope to build up speed, conditioning, and agility.  I wonder if there is a professional boxer/fighter out there that doesn't train with a rope?  Use it a method of warming up instead of the treadmill, incorporate it into a workout, use it as a cool down.  However you fit it into your workout routine you need to be doing it.  It took me about 6 months of casual practice to learn how to do double unders with confidence (two rotations of the rope for every one jump).  Most people build up to hundreds of single jumps, then one leg, crossovers, double unders, then combinations of them all.  Try it and have some fun.  How long to do 250 singles?  Max double unders?  Can you do crossovers for 1 minute? What about when you are fresh versus tired?  etc.
There are many ropes out there from the cheap old school beaded ropes (think kids playground) to the expensive Buddy Lee ropes ($30-$40ish) that are used and recommended.  I started with a Harbinger Trigger Handle ($10) rope. I like it because its simple, heavier, and slower, so I can control it easier but takes more effort, tires you out faster, and isn't very durable.  More recently I made purchases from http://www.buyjumpropes.net and they offer various styles at good prices.  I would recommend both the Boxer's Training Jump Rope (~$10 shipped) or the Cable Freestyle Rope (~$16 shipped).  There aren't too advanced to start out with but are definitely lighter and faster then whats offered at your local Sports Store so you need to move those wrists and legs faster!  Also these can easily be adjusted in length and the cord doesn't get kinked or tangled, and durability looks good so far.  

Cool inspirational Video :Buddy Lee Power Jump Double-Under