Summon Demon/Elemental.  It's the most flexible spell, despite the risks.<br/>Cirrus Skiff will enable you to deploy to the party's location in an emergency, or give us an airlift in same.  Curse of slavish humility cast through an arcane link can end a social problem (provided the party can get an arcane link).<br/>Eye of Alliance gives the party major advantages by creating an arcane link between the sorcerer and all party members, which has all kinds of possibilites.  (it also enables short telepathic and sensory messages).  Forging the Sworn Brotherhood is a powerful spell in general, and can help deal with the wooblieness that eye of alliance might otherwise cause.<br/>Purifying Flame makes for a good counter if we have to worry about getting attacked by poison and sickness.  It depends on whether the GM actually remembers that having mortals coat their weapons in coral snake venom is a fairly powerful and cost effective way to fight exalts.<br/>Shadow Summons is a fun way of annoying the hell out of someone, and can also enable an assassination which is really really hard to defend against.  (the only real way is to have someone right there ready to cast emerald countermagic)<br/>Spirit Sword can be a really good spell if it can be cast through an arcane link, although that might be tricky to manage.<br/><br/><br/>For artifacts, you may want to consider trying to get a pair of identical tiny boxes for which one thing put in will appear in the other box no matter where it is in creation and vice versa.  That would enable the party to funnel arcane links to you.