[Taqwus]

There may be specific spells to shoot for. For a nation with good archers, for instance, Wind Guide and Flaming Arrows are obvious picks.
For R'lyeh, Thaugmaturgy 1's Returning might save your Void Summoner; later on, Ritual of Returning will help. Thaug also provides Paralyze, if memory serves, a strong spell for astral nations.
For Jotunheim/Utgard, those Astral/Death seithkona are just begging to be able to cast Nether Darts, but that's fairly high level.
For Abysia, Conjuration research provides access to Summer Lions, which make an unbreakable, ethereal front line. Just avoid the temptation to be a one-path nation, however...