In another thread he mentions Tutu, so I suppose the OP has quit the monk game and has started anew with Tutu'd original BG1.
I'm not an expert on the game, but have played through them several times, mostly with mage-types (it's more fun).
Usually not a fan of touch spells since you need to go into the thick of things and actually hit, but Vampiric Touch can be really nice for boosting HP and causing damage. Early in the game, Sleep is great for taking out hordes of weak foes, or dangerous foes early on. Magic Missile is quite nice, but only later on when you get several missiles. I love Fireball. Well placed Fireballs can really mess up a group of enemies. A nice way to kick off combat. You can get Necklaces with them too, so everybody can wield them if you want (and then there are the potions...).
Once you get into intermediate levels territory (early BG2 really), Cloudkill and Breach are excellent, the latter obviously to take down mage defences. Lower Resistance can be vital in some fights. Stoneskin is long-lasting and offers excellent protection, so I prefer to walk around with it at all times.
Greater Malison is good early in combat, and after that you can hit with crowd control of some kind. Haste is good in tough fights to increase damage output. Just be aware that you'll be fatigued afterwards, so you may want to rest then.
Melf's Minute Meteors is excellent too. When you don't want to throw more damage spells, to preserve them for later, or you have taken down mage defences, you can attack from range with these babies. At high levels you get a heap of them, and they will do some damage even against well-protected foes.
Protection from Evil (10 radius) is excellent too, and should be a maintay when buffing up. Quite long-lasting.
On the first few levels, Web is great for crowd control. Web+Fireball is a neat and efficient tactic.
Not for combat, but I love to walk around with heaps of Identify spells, especially after you find that item that doubles (?) the amount of level 1 spells. Saves you some money on identifying items. And since there are few truly useful level 1 spells, you don't lose much by a heap of Identify spells.
What you prefer depends on your playstyle, and I've talked here more from a typical mage point of view rather than a fighter-mage (because I've never played as one). As a fighter-mage, I assume crowd control and fireball is of less importance, and you want to buff up and deal out lots of hurtin' instead, going into the thick of things instead of causing havoc from the back of the pack.
I don't agree with everything in there, but it's a good guide for the more useful spells:
http://www.forgottenwars.com/oogi/index.htm