COMPARISON OF ADJECTIVES
IRREGULAR COMPARATIVES AND                     SUPERLATIVES

These adjectives have completely irregular comparative and superlative forms:
 
 

Adjective Comparative Superlative
Good Better Best
Bad Worse Worst
Little Less Least
Much More Most
far   further/farther furthest/farthest

Original source: http://www.edunet.com/english/grammar/ADJECTIVES1.cfm