Gez said:My first reaction was to open the Sovelior/Sage SRD because it's kept updated with errata, but, of course, beholders aren't in the SRD...
In the 3e MM (2000), the Beholder's caster level is 13, and there aren't any '14' in the write-up. So, I'd say it is CL 14, because there's no way it would be a cut'n'paste error or leftover from the unrevised edition. While for CL 13, it is possible. CL 14 had to be entered voluntarily by the writers.