WordNet (r) 3.0 (2006):

crack up
    v 1: suffer a nervous breakdown [syn: crack up, crack,
         crock up, break up, collapse]
    2: rhapsodize about
    3: laugh unrestrainedly [syn: break up, crack up]

Moby Thesaurus II by Grady Ward, 1.0:

229 Moby Thesaurus words for "crack up":
   ablate, accident, appulse, atomize, bang, bang into, bankruptcy,
   blow, brain disease, break down, break up, breakage, breakdown,
   breaking up, breakup, brunt, bulldozing, bulling, bump, bump into,
   burn out, calamity, cannon, carambole, carom, carom into,
   carry away, casualty, cataclysm, catastrophe, cave, cave-in,
   circulatory collapse, clash, collapse, collide, collision,
   come apart, come into collision, come off, come undone,
   come unstuck, concuss, concussion, confront each other, consume,
   contretemps, corrode, crack, crackup, crash, crash into, crippling,
   crumble, crumble into dust, crump, crunch, damage, dash into,
   debacle, decay, decompose, destruction, detriment, diffusion,
   dilapidation, disablement, disaster, disintegrate, disintegration,
   disjoin, disorganize, dispersal, disrepair, disruption,
   dissolution, dissolve, draining, droop, drop, emotional disorder,
   emotional instability, encounter, encroachment, erode, exfoliation,
   exhaustedness, exhaustion, faint, fall foul of, fall off,
   fall to pieces, fatigue, fission, flag, flip, fly apart, foul,
   fragmentation, functional nervous disorder, gasp, get loose,
   get tired, give out, give way, go crazy, go haywire,
   go into hysterics, go mad, go to pieces, grief, grow weary,
   hammering, harm, hit, hit against, hobbling, hurt, hurting, hurtle,
   ill hap, impact, impairment, impinge, impingement, incapacitation,
   infringement, injury, inroad, insanity, jade, knock, knock against,
   lose courage, lose self-control, loss, maiming, maladjustment,
   manic-depressive psychosis, mauling, mayhem, meet, meeting,
   melancholia, mental disorder, mental illness, misadventure,
   mischance, mischief, misfortune, mishap, molder, mutilation,
   nasty blow, near-miss, nervous breakdown, nervous disorder,
   nervous exhaustion, nervous prostration, neurasthenia, neurosis,
   onslaught, pant, paranoia, peel off, percuss, percussion,
   personality disorder, peter out, pileup, play out, poop out,
   problems in living, prostration, psychosis, puff, puff and blow,
   ramming, reaction, revolution, ruination, ruinousness, run down,
   run into, run out, sabotage, scaling, scathe, scattering,
   schizophrenia, shattering, shipwreck, shock, sickening, sideswipe,
   sink, slam into, sledgehammering, smack into, smash, smash into,
   smash up, smash-up, smashing, smashup, social maladjustment, split,
   spoiling, spring apart, staggering blow, start, strike,
   strike against, succumb, thrusting, tire, total loss, tragedy,
   unravel, washout, waste away, weakening, wear away, weary, wheeze,
   whomp, wilt, wrack, wreck