[Fate]

Most combat spells don't require gems (its just the army killing/battle field wide/blood magic spells that require gems).

That said, those same spells are mostly limited to use as buffs on your thugs/SCs or spamming.

Low level Alteration buffs (especially E/N/S) can be spammed on your elite/trampling troops to great effect (and can also turn that chaff army into an elite uber-force). Mid-level evocations (and even some low ones) can make a real difference, especially when you hit a critical mass of mages (varies depending on spell/target, but I find few early armies can withstand, say, 3-6 mages spamming Thunderbolt).

You might also want to look into Linebacker communions (see Baalz's excellent communion guide). Any nation with strong (in melee) astral commanders (admittedly, not many) or access to quick, cheap matrices can make good use of them.

For death nations (I'm looking at you, LA C'Tis) I have been soundly dumbfounded more than once by a simple skelly spam (Ench 4 I believe).

Thaum 4 also gives nice things like gift of flight, regeneration, battle frenzy (use at your own risk).

In general, though, I find that gem-less spells are weaker than their gem-costing counterparts. And you know what you lack in quality you must make up in quantity...