What are good spells or feats to complement Summoning spells?

[Shard O'Glase]

Haste on yourself is key since it will reduce the casting time from one round to full round action.

I like the chain spell feat idea. You can chain buff spells onto your party and the summons so the buff spells aren't wasted in 10 rounds when the summons go and it does buff your summons. Also chain summon can summon swarms of low level monsters, for example as a 7th level slot it can summon(at 14th level when you get 7th level slots) 15 level 4 monsters or 15 d3 level 3 monsters or 15 d4+1 level 2 monsters. Now think about overbearing your enemies. Oh and make sure you speak infernal and celestial so you can give more complex orders(like overbearing) to these things.

 

[Pielorinho]

Also chain summon can summon swarms of low level monsters, for example as a 7th level slot it can summon(at 14th level when you get 7th level slots) 15 level 4 monsters or 15 d3 level 3 monsters or 15 d4+1 level 2 monsters.

Very cool idea, but chain spell as describe in Tome and Blood won't do this: it only works on spells with a single target, and summoning spells have an effect, not a target.

You could possibly write up a different feat to achieve this effect. I've loaned out my copy of Relics & Rituals, so I can't say whether their version of a chain spell feat would work.

Daniel