i have a brain for you , my sister's boyfriend as one he doesnt use so that would be perfect ......
.............sorry when i saw the thread title i just couldnt resist
joke asside the color changing brain like frankie's girl mentioned is very cool i have one in my mad lab , the batteries usually work all evening too ....
or the ones at dollar stores that grow in water do a great job (at least the ones i found here do ),espacially for the texture if you have kids touch it i have 5 or 6 in a uge water jar for the past 2 years and so far so good .