Well now, low-level mages are not complete without Chromatic Orb. Next comes the Skull Trap as it has the same radius as a fireball, but almost nobody in the game has slashing resistance over 5%, while fire resistance is very often found. And it doesn't have a maximum danage, as opposed to the Fireball's 10d6. Next to all the sequencers and contingencies, we have the one and only Abi Dalzim's Horrid Wilting, which has a potential to do more damage than a Meteor Strike or a Red Dragon's Breath. Timestop is a must have, and Improved Alacrity really helps in Timestops(imagine bombarding an area with 9 Skull Traps in 1 second). Banshee's Wail is also cool

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Other effect spells include the Dispell, Spell Thrust, Magic Resistance(with which you only need to cast one Lower Resistance), Lower Resistance, Greater Malison(one of the most usefull spells in the game) and the Symbol/Power Word: Stun. Summons are rarely usefull for anything but drawing fire, and I almost never invest in those.
Also mind that this is only the arcane list of spells, the divine also has some nicities. Not as near as mages, but some are nice(like the amazing no-save Implosion).