hi Shannon, if any of it is designer goods and in excellent condition, you might try some of the high-end second-hand shops around Seefeld or Hottingerplatz. Otherwise, there are containers where you can pack the clothes in a bag and drop them off. I don't know where the one nearest to you is, but ours is next to the glass recycling bins. Be careful to check what you may and may not put in though: some take shoes and leather goods, some don't.
Here's one that lets you search for container closest to you:
http://www.texaid.ch/301.0.html