I would have to say it depends on your playing style. If you are roleplaying your character through and through (my mage is all about justice and helping out those in need) then go with whatever strikes your fancy (I have one point in Freeze, Elemental Hail, and a few others. I have definitly put in alot on Lightning, Meteorstrike, Elemental Bolt and others as these fit with my characters background I have made for him.) If your more for crushing your way through the game Elemntal Bolt is powerful though not very mana efficient (imo), Meteorstrike gives good damage, low mana cost and you can fire 'em off as fast as you can click a button. Lightning is pretty neat, though its usefulness could be debated, but I have found its good for holding an enemy back while I quaff a potion or two. I would say your most useful spells would be Freeze, Meteorstrike, Deadly Discs, Poisonous Cloud, Hellspikes and Elemental Bolt (though slow moving you can stream them at an opponent and it causes lots of pain and hurt for you target and whatever else is in the way.) Hope this helps, as I have not gone very far in the game (level 31 currently) except just wandered around enjoying the scenery and killing undead and orcs. I have no idea what will help you endgame but these spells have definitly made my mage's life easier. I would say with that many skill points, go with some of the recommendations people make here and choose any others that catch your fancy. Hope this helps a little.
Dunyain
