[Gregstrom]

I may be able to add a couple of pointers.

It is often said that the best summonable creature is the Seraph. It's rather expensive, though. To try it you'd need to be playing as MA Pythium or MA Marignon.

Quite a few good summons are in the Death school, so you could try playing as a Death heavy nation - EA or LA C'tis, for example. You can also reanimate undead with clerics of several nations. It's another form of summoning, and very useful.

Again as noted above, Blood has a lot of entertaining summons available. Jotunheim and Abysia have some Blood for checking out the basic summon roster there.

EA Mictlan and Lanka have a wide range of powerful national Blood summons, and for Mictlan at least you really want to be using them to get the best out of the nation.

Finally, MA R'lyeh has an interesting summon site in its capital and might be worth a look-in.