Undead have no special ability to overcome invisibility just because they are undead. Glamers are not mind-affecting spells.
In addition to all of the magical and special sensory means of overcoming invisibility, greater or otherwise, that have been mentioned, there is also rather common Listen check. To quote the SRD:
Note the hyperbole in the second to the last sentence. It's not practically impossible to pinpoint the location of an invisible creature in certain circumstances. An invisible spellcaster, for example, is going to have to at least talk with a strong tone of voice to cast spells (barring Silent Spells). This is a DC 0 Listen check, not counting modifiers for range (-1 per 10 ft.) or barriers.
Since we're talking about a sorcerer able to cast greater invisibility, let's assume an 8th-level party. Now consider the first CR 8 monster I found in the MM: an efreeti. This creature has Listen +15. It can probably make the Listen check to pinpoint the invisible sorcerer's location easy enough. Sure, it still must contend with the 50% miss chance, but that's okay. Two 12th-level scorching rays (one Quickened, one as a standard action) ought to at least get the sorcerer's attention.
In short, greater invisibility is far from a game killer. There are plenty of counters written into the rules.