In my opinion Mage spells should stay within the Mage's primary school.
Thus as an Arcane, Fire, or Frost Mage.. you only cast spells of that type.
Understand that I am not implying that you miss out on spells you need, but rather they become something else with each tree.
Some non-combat spells like Time Warp, and Evocation are fine as is.
Arcane
Arcane Explosion:
[Winding Ice]
Causes an explosion of ice shards around the caster, causing frost damage to all targets within 10 yards.
[Billowing Fire]
Causes an blast of flame around the caster, causing fire damage to all targets within 10 yards.
Fire
Fire Blast:
[Ice Whip]
Whips the enemy for frost damage, and slows them by 30% for 2 seconds. (30yd range, 8s cooldown)
[Arcane Lash]
Blasts the enemy for arcane damage, and pulls the target towards the caster 5 yards. (45yd range, 8s cooldown)
Scorch:
[Arcane Salvo]
Blast the enemy arcane damage. Being locked out of Arcane does not cause you to be unable to cast Arcane Salvo. (40yd range, 1.5s cast)
[Ice Shard]
Embeds a shard of Ice in the target dealing frost damage over time with no initial damage, being locked out of Frost does not cause you to be unable to cast Ice Shard. (40yd range, 1.5s cast)
Flamestrike:
[Snowfall]
Deals frost damage in an 8y radius over 8s, no initial damage, any enemy in the snowfall is slowed while inside the area, only one snowfall may be active at a time (2s Cast, 35y range)
[Spatial Rift]
Blasts an 8yd radius with arcane damage, deals arcane damage every second to enemies in the area of effect for 5 seconds, enemies that remain in the rift have their chance to hit reduced by 5% while inside the rift. (2s Cast, 30y range)
Flame Orb:
[Arcane Spheres]
Launches a series of 3 Arcane Spheres forward from the Mage's position, the spheres will cast Arcane Explosion every 2 seconds until they reach their destination causing Arcane Barrage initial blast damage to the target. (40yd range, 1 minute cooldown)
Frost
Cone of Cold:
[Volcanic Surge]
Targets in a cone in front of the caster are slowed by 60% for 8 sec. (10s cooldown)
[Arcane Ripple]
Targets in a cone in front of the caster take arcane damage and are slowed by 60% for 8 sec. (10s cooldown)
Frost Nova:
[Flame Wave]
Blasts enemies near the caster for Fire damage and melts them in place for up to 8 sec. Damage caused may interrupt the effect. (25 second cooldown, 15yd radius)
[Arcane Burst]
Sends out a pulse of Arcane energy dealing damage and immobilizing them for 5 sec. (25 second cooldown, 20yd radius)
Ice Block:
[Shield of Cinders]
You wall yourself behind seething flame, protecting you from all physical attacks and spells for 10 sec, but during that time you cannot attack, move or cast spells. (Instant Cast, 5 minute cooldown, Blast Wave is triggered if an enemy attacks you while under the effects of Shield of Cinders {radiating outwards from you, but limited to 5yd radius})
[Fold Reality]
You fold time and space around your body, protecting you from all physical attacks and spells for 10 sec, but during that time you cannot attack, move or cast spells. (Instant Cast, 5 minute cooldown, all unfriendly spells cast on you will be reflected, however healing taken in this state is reduced by 25%)
Ice Lance:
[Ashen Spear]
Deals Fire damage and applies a stacking debuff to the target. Each application slows the target by 10%, stacks up to 3 times. (25yd Range, Instant Cast)
[Arcane Javelin]
Deals Arcane damage and knocks the target back 10 yards. (40yd range, consumes a proc of Arcane Missles to cast, 20s cooldown)
Blizzard:
[Blazing Embers]
Burns the ground every 1 second for 8 seconds in an 8 yard radius. (Channeled, 40yd range)
[Arcane Void]
Deals Arcane damage every 1 second for 8 seconds in a 10 yard radius (Channeled, 40yd range) (if cast for full channel time applies a field of arcane energy to the target area lasting 8 seconds, any target that enters this field has Slow applied to them)
Ring of Frost:
[Binding Flames]
Ignites the ground, taking 3 sec to form. Enemies entering the area will be immobilized in a vortex of fire for 10 sec. Lasts 12 sec. 10 yd radius. (All existing Fire damage over time spells persist through this effect, additional damage taken will cancel it)
[Stop Time]
Stops the progression of events in it's area of effect, taking 3 sec to form. Enemies entering the zone will have events cease for 10 sec. Lasts 12 sec. 10 yd radius. (All DoTs, HoTs, incoming healing spells and damage cease until this effect ends)