Galio is a pretty decent threat to Veigar, but he doesn't have as much offensive pressure as some of his other counters so Veigar's likely to still be able to farm, though he won't be netting any kills early on.
I'd say Veigar's worst matchup is against Syndra, just because she has all the CC, range and poke she needs to fight him early on and COMPLETELY deny him from getting any farm of sorts, since the second you passively step in she's poking you with spheres left and right. Other bad matchups for Veigar would be Zed and Orianna, IMO; essentially champs that have both the poke and the range (or slight durability in Zed's case) needed to push him out. I'd argue Zed is less potent as a counter, however, because Veigar can build around him if he rushes tear for the mana and then goes for Zhonya's, and smarter players will probably be able to avoid his Qs more easily, since they're more telepathed and have a smaller radius than Syndra's or Orianna's Q.