As with all carnivores, the main consideration driving the behavior of large theropods like allosaurs and abelisaurs was the availability of prey. As a rule, carnivorous dinosaurs were much less common than herbivorous dinosaurs (since it requires a large population of herbivores to feed a smaller population of carnivores). Since some of the hadrosaurs and sauropods of the Jurassic and Cretaceous periods grew to extreme sizes, it's reasonable to conclude that even the bigger theropods learned to hunt in packs of at least two or three members.
One major topic of debate is whether large theropods actively hunted their prey, or feasted on already dead carcasses. Although this debate has crystallized around Tyrannosaurus Rex, it has ramifications for smaller predators like Allosaurus and Carcharodontosaurus as well. Today, the weight of the evidence appears to be that theropod dinosaurs (like most carnivores) were opportunistic: they chased down juvenile sauropods when they had the chance, but wouldn't turn up their noses at a huge Diplodocus that died of old age.
Hunting in packs was one form of theropod socialization, at least for some genera; another may have been raising young. The evidence is sparse at best, but it's possible that larger theropods protected their newborns for the first couple of years, until they were big enough not to attract the attention of other hungry carnivores. (However, it's also possible that some theropod kids were left to fend for themselves from birth!).
Finally, one aspect of theropod behavior that has received a lot of attention in the popular media is cannibalism. Based on the discovery of the bones of some carnivores (such as Majungasaurus) bearing the tooth marks of adults of the same genus, it's believed that some theropods may have cannibalized their own kind. Despite what you've seen on TV, though, it's much more likely that the average allosaur ate its already-dead family members rather than actively hunting them down for an easy meal!
Here's a list of the best-known large theropods of the Mesozoic Era; just click on the links for more information.
Abelisaurus "Abel's lizard" has been recontructed from a single skull.
Afrovenator One of the few carnivores ever to be dug up in northern Africa.
Allosaurus One of the most common predators of the Jurassic era.
Baryonyx Long story short: you wouldn't want to clip this dino's claws.
Carcharodontosaurus Its name means "great white shark lizard." Impressed yet?
Carnotaurus The shortest arms of any meat-eater--and horns to match.
Ceratosaurus This primitive carnivore is hard to classify.
Concavenator This large theropod had a bizarre hump on its back.
Cryolophosaurus This crested carnivore was once known as "Elvisaurus."
Edmarka This may have been a species of Torvosaurus.
Ekrixinatosaurus Its name means "explosion-born lizard."
Eustreptospondylus A close cousin of Megalosaurus.
Fukuiraptor One of the few carnivorous dinosaurs ever to be dug up in Japan.
Gasosaurus Yes, that's its real name, and not for the reason you think.
Giganotosaurus Not quite a "Gigantosaurus," but close enough.
Gojirasaurus This early predator was named after Godzilla.
Ilokelesia A primitive abelisaur from South America.
Indosuchus This "Indian crocodile" was actually a dinosaur.
Kaijiangosaurus This might have been the same dinosaur as Gasosaurus.
Lourinhanosaurus This hard-to-classify theropod was discovered in Portugal.
Majungatholus Fairly--or unfairly--known as the "cannibal dinosaur."
Megalosaurus The first dinosaur ever to be discovered and named.
Megaraptor Despite its name, it wasn't really a true raptor.
Monolophosaurus This Jurassic predator had a single crest on its skull.
Noasaurus Were this predator's giant claws on its hands, or on its feet?
Piatnitzkysaurus Its teeth were as sharp as its name is funny.
Poekilopleuron It may (or may not) have been a species of Megalosaurus.
Rajasaurus This "prince lizard" lived in what is now modern-day India.
Rugops This wrinkly-faced carnivore probably fed on abandoned carcasses.
Siamotyrannus Despite its name, it wasn't a true tyrannosaur.
Sinraptor Despite its name, this allosaur wasn't any better or worse than other dinosaurs.
Spinosaurus This dino was distinguished by the sail-like structure on its back.
Suchomimus A fish-eater with a distinctly crocodilian profile.
Torvosaurus One of the largest predators of Jurassic North America.
Tyrannotitan We know very little about this fearsomely named dinosaur.
Xenotarsosaurus A poorly understood abelisaur from South America.
Xuanhanosaurus You didn't think there'd be an "X" on this list, did you?