TalentSwitch

This addon automatically switches your talents on your actionbars when you change talents. It will also parse your macros and substitute in your active talents over any inactive ones from the same tier.

Also allows the saving of commonly used builds.

Usage and known issues:
Automatic talent replacement will only occur if you select an "active" talent. Passive talents will not be swapped in – the addon will leave the active talent from your bar as a reminder of which slots were in use. If that slot remains unchanged, it will be reused when you reselect an active talent from that tier.
Example:
I swap from Diffuse Magic to Dampen Harm. Diffuse magic is automatically taken off of my bars and replaced with Dampen Harm.
I then swap to Healing Elixirs. Dampen harm remains, but is inactive.
I then switch back to Diffuse Magic. Diffuse Magic is palced on my bar where Dampen Harm used to be.

The macro parser only works for the correct capitalisation of talent names. This means that you can "opt-out" of the macro update by using all lower-case.
Example:
I have Diffuse Magic and Tiger's Lust, and the following macro:
#showtooltip
/use [nomod] Diffuse Magic
/use [mod] tiger's lust

I switch to Dampen Harm and Celerity, and the macro automatically becomes:
#showtooltip
/use [nomod] Dampen Harm
/use [mod] tiger's lust