WordNet (r) 3.0 (2006):

pop up
    v 1: appear suddenly or unexpectedly; "The farm popped into view
         as we turned the corner"; "He suddenly popped up out of
         nowhere" [syn: crop up, pop up, pop]

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "pop up":
   accomplish, achieve, appear, appear unexpectedly, approach, arise,
   arrive, arrive at, arrive in, attain, attain to, be received,
   be unexpected, bechance, befall, betide, blow in, bob up,
   break forth, break water, burst forth, chance, check in, clock in,
   come, come along, come forth, come in, come into being,
   come into existence, come on, come to, come to hand, come unawares,
   come upon, creep up on, crop up, debouch, draw on, erupt,
   fall upon, fetch, fetch up at, find, flare up, flash,
   flash upon one, float up, fly up, fountain, gain, get in,
   get there, get to, gleam, gush, hap, happen, happen along,
   happen by chance, hazard, hit, hit town, irrupt, jet, jump up,
   leap up, make, make it, materialize, pounce upon, present itself,
   pull in, punch in, reach, ring in, rocket, roll in, shoot up,
   show up, sign in, skyrocket, spring up, spurt, start up, surface,
   time in, turn up, upleap, upshoot, upspear, upspring, upstart,
   vault up