Summon Nature's Ally and Summon Monster (all their iterations) are your best choices.
I would also suggest grabbing the Corrupt Summons spell from somewhere if you are evil (because creating an "Only Evil creatures can be summoned here" is lulzy, especially since the summoned creature will attack their summoner if they aren't evil.) Other than that, I would really suggest the Summon Elemental reserve feat at 9th, since anything that affects Summon Monster affects it (so your bog-standard Augment Summons,
which you are taking, your arguments against it are invalid also boosts your free Elementals as well.)
Cloudy Conjuration is nice for a little free BC, iirc.
Other than that, we can't give you many specifics without you telling us a bit more about the character idea; there are a lot of ways you can go when it comes to summoning as an Archivist (you can draw on all the best summoning spells in the game, and most of those fall into different categories that need different tweaks.)
Of course, if you can convince the DM that summoning creates creatures, you might be able to swing Corpsecrafter et al for the Summon Undead line of spells; but that is major houserules right there, so it ain't likely.
One final way: see if you can have a divine Shadowcraft Mage OK'd by the DM. Play a Gnome Archivist 5/Shadowcraft Mage (I think you can get in at that level; haven't checked in a while...) and then just use Silent Image to cast whatever summoning spell you need; you have the spell-list for it
.