Actually, the other two pantheons from D&Dg are tight pantheons as well, and a cleric can worship the whole pantheon, just as they can with the Asgardian pantheon.
So, we have:
The Sovereign Host
The Dark Six
The Olympian Pantheon
The Pharaohic Pantheon
The Asgardian Pantheon
Five pantheons, without looking very hard.
Also, IIRC, in Faiths and Pantheons, each of the races has a racial pantheon with four to eight racial gods (always including the Greyhawk standard racial deity). I don't know if any of them are worshipable as a pantheon, but it wouldn't take a DM any more than five minutes to work up how to do it in his own game.
I think Eberron's approach is the most "realistic," in that you have some individual deities, as well as some pantheons. This most closely mirrors what we've seen in the real world.
Am I the only one bothered that their 'pick whole pantheons thing' only applies to the real world? Is it that hard to just clump gods together? :/
Or at they all asocial loners? :O
Keep in mind that the Dark Six are actually splintered off the Sovereign Host, they originally were the 'darker' gods of the pantheon before differences led to a schism proper. However, Eberron has more than that.
That said, Eberron is one of the better settings for fantasy religions, which just serves to highlight how limited the pantheons in most of D&D are. You have:
-GrecoRoman Pantheon in the form of the Sovereign Host and the Dark Six, where everyone worships every friendly god based on their needs, and propitiates enemy gods to deflect them. The priesthood is largely specialized, but they do honor the rest of the pantheon as needed, and there is a means to act as a pantheistic cleric within the limitations of the D&D system.
-Monotheistic Silver Flame, in the best traditions of the knights templar.
-Ancestor Worship for the elves
-Secret cults in the form of the Blood of Vol
-Extremist/Doomsday cults in many stripes.
-God-Emperor(to be) in the form of the Lord of Blades
-Brainwashing cult for the Path of Inspiration
-Buddhist-like philosophical cult for the Path of Light
-Weird stuff like the Becoming God
Pretty much the only one I can't find is shamanistic, which D&D doesn't mechanically support very well to begin with.
Contrast instead, Greyhawk or Forgotten Realms as the big names. Followers of a given god do so exclusively, heck, in FR, never dedicating to a deity leads to a bad afterlife, which in turn gives you a fairly unbalanced personalities in any faith. Gods are added alone, even if they are nominally in a pantheon, furthering their causes while blind and deaf to their pantheon-mates. The smith-god makes stuff, but instead of forging divine arms for his allies, he simply creates without purpose, etc. People worship one god exclusively, to varying degrees of zeal.
That's the issue, more or less. The exceptions are pretty much only when they import real world pantheons...which are naturally pantheistic because that's how it is over here.