Aegir, though not an integral character in the great Eddic myth, appears in several different Eddic Lays, primarily in the Grimnismal, Lokasenna and Hymiskvidha. We know from the Grimnismal 46 that the gods sit "on Aegir's benches at Aegir's feast". Hymiskvidha tells of the acquisition of Aegir's cauldron, large enough to brew ale for all of the gods. In Hymiskvidha 2, Aegir is called the "sea god". Finally, in the Lokasenna, Aegir and his servants Fimafeng (Handy) and Eldir (fire-stoker) play host to all of the gods. Aegir's hall was filled with shining gold, bright enough to serve as light, and the cups in this hall filled themselves with ale. It was also a frithstead, where no blood could be spilled (though Loki slew Fimafeng just before the events of the Lokasenna unfolded).
In addition to these Eddic lays, we also looked at an excerpt from Tacitus' Germania which talks in detail about the feast in Germanic culture.
Finally, as always, H.R.E. Davidson is a invaluable source for us and many Asatru kindreds. In her book Gods and Myths of Northern Europe, Davidson has a chapter on "The Gods of the Sea", including a section on Aegir and Ran.
There are three distinct themes surrounding Aegir. He is plainly called a god of the sea, is thought of as a god of brewing, and presides over the feasts that all the gods attend. There is a clear relation between him being a god of brewing and the host to the gods, but does the "sea god" title fit? Hollander suggests that there was a perceived relation between the foam of breaking waves and of brewing ale. The Norse viewed the sea and alcohol as dual natured and potentially dangerous. The sea could be violent and deadly, dragging sailors to their death, or placid and calm, promoting trade and exploration and bringing in wealth. Alcohol could be inspiring, as Kvasir was, or could lead to violence, as Tacitus noted sometimes happened when the Norse drank.
Aegir's hall does not necessarily reside in Asgard, as it is not listed in the Grimnismal, though it is described in some detail in the Lokasenna, thus one cannot claim with total assurance that he is a member of the Aesir or Vanir (though as a Jotun, he is no less deserving of worship).
In the Lokasenna, Aegir is mentioned many times, both by the gods themselves, and by the narrator who describes his hall and the events leading up to the drama. However, Aegir himself does not speak at all in the poem. This cannot be an accident, since every other god mentioned, even Frey's servants, and Eldir, Aegir's servant, get their chance to speak in the lay. This speaks to the responsibility of the host, we think, to maintain neutrality with quarrels in his/her home. Perhaps he does not get involved with the flyting because he is, as the host, sober, and maintains the social niceties that Tacitus noted seem to fail when sumbel starts.
It should be noted that the very last words recorded by Loki are a curse upon Aegir:
65 "Ale madest thou, Aegir, but not ever shalt henceforth brew for a banquet: all that thou hast this hall within may flames set on fire and burn on thy back!"
The Trickster, it seems, could not return the hospitality shown to him by Aegir. Because these are the last words spoken by Loki, it can perhaps be assumed that this curse, out of all the ones spewed by Loki, was the straw that broke the camel's back. If Skadhi's previous prediction of Loki's fate came true, then it might be assumed that Loki's curse comes to pass, as well, and that Aegir's hall is destroyed after the flyting (maybe Eldir was a little too much of his namesake). If so, it is a chilling, yet poetic prelude to Ragnarok, when the warmth and friendship of Aegir's halls are dead to all the worlds.
Finally, in the Lokasenna, Aegir is referred to as "Gymir", which translates to "The Binder". Ideally, the feasts that Aegir hosts "bind" communities together.