Amethyst Crystal (525g)
Stats: 5% CDR
Recipe: Amethyst Crystal (525g) + 625g = 1150g (or make it double Amethyst Crystal)
Stats: 12% CDR, 7% Movement Speed and [+10 Magic Penetration OR +10% Spell vamp]
Recipe: Rigor (1150g) + Rigor (1150g) + 575g = 2875g
Stats: 25% CDR, 15% Movement Speed and [+25 Magic Penetration OR +25% Spell vamp]
These items kill three birds with one stone.
# Movement speed for casters (although I respect they possibly don't deserve any),
# If spell vamp, an item AD Casters can buy without wasted stats
# CDR without mana/mana regen (on a caster item), which players have been asking for.
They consume a slot without providing any damage, which I feel is a suitable balance... or at least a fair trade. I also think the lack of damage at all stages justifies nothing being unique, but any amount of the stats could be made unique.
Due to casters lacking attack speed and critical strike, I had to create a "basic item" that would build into these. Feel free to propose alternates. The Amethyst Crystal could be used in the recipe for other items such as Brutalizer (Long Sword + Amethyst Crystal, for example). Or it could not be intergrated into existing items at all.
Spell vamp or magic pen? Magic doesn't have a equivalent to critical strikes.