WordNet (r) 3.0 (2006):

run across
    v 1: come together; "I'll probably see you at the meeting"; "How
         nice to see you again!" [syn: meet, run into,
         encounter, run across, come across, see]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "run across":
   alight upon, blunder upon, bump into, chance upon, come across,
   come among, come on, come up against, come upon, confront,
   discover serendipitously, encounter, fall across, fall among,
   fall foul of, fall in with, fall upon, happen upon, hit upon,
   light upon, meet, meet head-on, meet up with, meet with,
   pitch upon, run into, run smack into, run up against, run upon,
   stumble on, stumble upon, tumble on