Cleaner - the cleanest
cheaper - the cheapest
faster - the fastest
slower - the slowest
higher - the highest
smaller - the smallest
stronger - the strongest
weaker - the weakest
taller - the tallest
shorter - the shortest
longer - the longest
younger - the youngest
older - the oldest (elder - the eldest)
newer - the newest
larger - the largest
whiter - the whitest
bigger - the biggest
wetter - the wettest
fatter - the fattest
thinner - the thinnest
sadder - the saddest
happier - the happiest
uglier - the ugliest
dirtier - the dirtiest
drier - the driest
messier - the messiest