I use the wowhead client. It copies info from my character, pulls down info from the Blizzard armoury and merges the two together to form a wowhead profile. From that I can pull my character's talent build and click the 'use in-game' button to generate a command I copy and paste into WoW. This will instant populate my talent build. This also allows me to 'ninja' builds from other players or design builds offline to use in the game later.
Here is Lin's current paladin prot build:
/run t,p,a={2,13,32,42,53,83,91,102,112,121,132,141,151,161,171,182,193,201,1,3,23,32,53,62,}SetPreviewPrimaryTalentTree(t[1],GetActiveTalentGroup())for i=1,#t do a=t[i]if a<9 then p=a else AddPreviewTalentPoints(p,floor(a/10),a%10)end end