Code Collector Pro (on sale for US$9.99, normally $19.99) offers a snippet manager for your development needs. I bought myself a copy a few weeks ago, when it suddenly went on sale, and have spent the time since kicking its wheels.
I was surprised to find out how much I like it. It offers excellent language-specific contextual highlighting, flexible tag support and easy-to-use searching. Whenever you have a snippet you want to store, just add a new item, paste and edit its metadata.
I installed it into my Dock on day one, and it's been there ever since. I have not yet found a reason to close it, hide it or put it away. That's a big deal for me given how zealously I guard my permanent Dock items.
Previously, I've tried using special-purpose Xcode projects, TextEdit files and even Notes to organize code bits. I was never really satisfied with any of those solutions. Code Collector Pro was built specifically for these kinds of short methods and functions that don't fit into class categories or helper libraries and it's doing a grand job in keeping those labeled, readable and (most importantly) findable.