I don't see a problem with a Wizard/Fighter. I just tried making up a 10th Level Human Wizard with all the Fighter multiclass feats, and he seems pretty good. I gave him a Close Burst encounter power from the Fighter, the initiative boost Utility, and the level 1 Daily power that gives +2 Attack and +4 damage until the end of the encounter.
His Wizard powers are focused on Close Bursts and Blasts whenever possible. Having taken proficiency with Hide Armor, and having a massive Intelligence, he's got a 26 AC, which thanks to his magic armor, bumps to 28 when he's bloodied. His other Defenses range from 21 to 23. Against a Soldier of equal level, his defenses are great; they need an 11 to hit his AC, and that's if he's not popping out his Staff Implement AC boost or a Shield, Blur or Mirror Image spell to make him harder to hit.
So he wades into Melee, firing off Close attacks and his Fighter powers. He's got 9 Healing Surges, a fairly decent amount, and several magic item abilities that give him damage resistance. He has two magical greatstaves: One Lightning Weapon, and one War Mage Implement. His attack bonus is actually +12 with both spells and weapons. It's a little below a Fighter's, by maybe 3 or 4 points, but he can still hit high AC standard monsters of the same level with a 12, or a 10 if he gets flanks(which he should).
So in the end, we have a Wizard who can back up the front line while still fulfilling his role by popping out area attacks. He can even mark and get an attack boost once per encounter. He only has two powers that can't be used Close, (Stinking Cloud or Bigby's Icy Grasp and Mordenkainen's Sword or Wall of Fire), but those same powers generally give a long-term effect of some sort, allowing the Wizard to continue to use it with little penalty after using it once. Beyond that, he only has one single-target attack, his Fighter Encounter power Villain's Menace. This, however, allows his Close attack to deal extra damage to the target while still nailing everyone else in the process; not a bad effect.
Guess I'll post the full stat-block for him; I used the 16 14 13 12 11 10 array.
Name: Jim Lightmagic Class: Wizard Race: Human Level: 10
Hp: 59 Bloodied: 29 Surge Value: 14 Surges: 9
AC: 26(28 when Bloodied) Fort: 21 Ref: 23 Will: 21
Feats: Student of the Sword(2-Handed), Armor Proficiency(Leather), Armor Proficiency(Hide), Novice Power, Durable, Acolyte Power, Adept Power, Ritual Casting
At-Will: Magic Missile, Scorching Burst, Thunderwave*
Encounter: Burning Hands(1), Color Spray(3), Come and Get It(Fighter 7)
Daily: Villain's Menace(Fighter 1), Stinking Cloud(5) or Bigby's Icy Grasp(5)*, Mordenkainen's Sword(9)* or Wall of Fire(9)
Utility: Shield(2)* or Expeditious Retreat(2), Battle Awareness(Fighter 6), Blur(10)* or Mirror Image(10)
Magic Items: +2 Bloodthread Hide Armor, +2 Lightning Quarterstaff*, +2 Staff of the War Mage, +2 Cloak of Resistance
Str 16 Con 13 Dex 10 Int 20 Wis 11 Cha 12
*: Primary choice
If you're wondering why I chose single-target spells like Icy Grasp and the Sword, it's just because I like how the flavor of those spells matches with the character's design. Stinking Cloud and Wall of Fire are probably better choices.