In our Heroic Tier party fo four, the wizard is necessary. We all pray he gets a high initiative for the first round. (Improved Initiative, some dexterity and a Warlord help.)
One great combination is a Grasp of the Grave (5th) with Enlarge Spell and Destructive Wizardry for a wide and damaging zone plus daze for combat advantage, followed up by Icy Rays (3rd) on an Action Point (Human Action Surge and Tactical Warlord) to lock the biggest foes inside the zone while the fighter, warlord and ranger take out the front line.
Phantom Bolt, Ray of Frost and Thunderwave all affect the tactics of the battlefield very nicely, and they are at will (Human for three at-wills).
Sleep is good. Web is great. Horrid Whispers damages the foes, gives them -2 to attack and then knocks them prone for easy pickings by the fighter and the warlord.
Finally, any immobilization or slow spell is necessary for the end of the encounter when the dangerous evil magician inevitably tries to flee for another day. Or to make sure no scouts run away to warn the rest of the dungeon.
