WordNet (r) 3.0 (2006):

sympathize with
    v 1: share the suffering of [syn: feel for, pity,
         compassionate, condole with, sympathize with]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "sympathize with":
   accord, ache, agree, agree with, appreciate, assure, be affected,
   be in tune, be inspired, be involved, be moved, be sorry for,
   bear up, bleed, bleed for, care about, catch the flame,
   catch the infection, change color, cheer, chime in with,
   color with emotion, comfort, commiserate, compassionate,
   comprehend, condole with, console, correspond, cotton to, dig,
   ease, echo, empathize, empathize with, encourage,
   express sympathy for, fall in with, feel for, feel sorrow for,
   feel sorry for, feel with, get along, get along with, get on with,
   give comfort, grieve for, grieve with, harmonize, harmonize with,
   hearten, identify with, interchange, lament for, pity, put at ease,
   react, reassure, reciprocate, relate to emotionally, relieve,
   respond, respond to, set at ease, share, sing in chorus, solace,
   sorrow with, speak soothing words, sympathize, understand,
   understand one another, weep for, weep with