The only way to get working Homebrew on OS X 10.10 for now (10.10 beta was just released a couple of hours ago) is by using an special fork by @jacknagel available at https://github.com/jacknagel/homebrew/tree/rb2.
To install this working version of Homebrew just execute:
ruby -e "$(curl -fsSL https://gist.githubusercontent.com/jpincheira/bd3698fee46735fac252/raw/2c6a2f81927871c1a64e2dfbbc5eef451c71a9ac/homebrew.rb)"