The last good mage-slayer build I saw used the swiftblade PrC. It gets some really nice abilities, like making haste be (Ex), so it can't be dispelled and it gives you an extra standard action per turn. You also get Freedom of movement as an (Ex) ability, so it works even in an antimagic field. Once you get in reach of a caster cast Antimagic field on yourself and prepare an action to follow him if he moves. He will be helpless.

My favorite build: Scout3/ranger2/wizard2/abjrant champion3/swiftblade 10

Casts as a lvl11 wiz
18 BaB
low HP, but everything misses you 50% of the time
amazing speed
amazing initiative
+6d6 skirmish damage if you take Swift hunter and improved skirmish and your favorite enemies are never immune to it. Take favorite enemy arcanist acf and anything capable of casting will tremble before you.