+1 for the bionics I have the grey ones and the new white big foot ones:http://www.devaskation.com/Bionic-Bigfoot-Stoppers
They are both quite long lasting, the white ones are even grippier than the grey ones, stopping really quick (also great for running up ramps at the skate park
Down side of the above white ones is they have to be really tight, as they are not round, if they turn around mid play they might rub on your wheels and stop you rolling.
I also like the Moonwalkers, although smaller they were really bouncy, they probably lasted as long as the gum balls.
All the above ones are lighter than Gumballs which is nice
(and all non marking)
I think the roll line toes stops are supposed to be good too but never tried them x