i picked up a balance board the other week partly (and wrongly) to rehab an ankle but also to help improve with core stability, balance and proprioception. all of the latter have been instantly useful and i've only taken one header - it was a sore one it has to be said, so my tip of the day if using one of these is leave enough space to have a fall! here's some vids (look in hobo dan's video list of you want to see how to make one)
you can do tricks on them but you can also use them to support other core based moves. best dial in your skills first tho - i took the aforementioned header doing a squat like move!
in short, i'd highly recommend some version of one of these particularly if, like me, the years are ticking by and you're noticing that your balance isn't what it used to be. you don't have to get one of these larger boards - you could make a wee thing you could stand on while you're doing the dishes. five to ten minutes of this a day and you'll notice improvements in your core stability (no. this doesn't mean you'll get abs!) and, despite it being a fail on rehabbing my ankle, i still feel it's useful for improving proprioception in your joints
