Big - bigger - the biggest
mean - meaner - the meanest 
clear - clearer - the clearest
meek - meeker - the meekest
sweet - sweeter - the sweetest
red - redder - the reddest 
clever - cleverer - the cleverest
broad - broader - the broadest
dim - dimmer - dimmest 
thin - thinner - thinnest 
hot - hotter - the hottest
weak - weaker - the weakest
cool - cooler - the coolest
flat - flatter - the flattest
deep - deeper - the deepest
green - greener - the greenest
sad - sadder - the saddest
fat - fatter - the fattest
slim - slimmer - the slimmest
wet - wetter - the wettest