Lifehacker's Texter is the only standalone one I know of. It's free, open source, and easy to use.
Also, if you have a background in programming, AutoHotkey might be a viable option. Texter has a GUI so thats probably your best choice.
Personally, I use vim for coding, so I use a combination of snipMate and sparkup for writing code. I used to use Textmate when I had a Mac, but when I went to Windows, I used E Text Editor for a bit. It's a feature for feature port of Textmate to Windows, and if you love Textmate, you'll be right at home.
But since I've discovered vim and sparkup/zen coding, I've had very little use for snippets anymore. It' so much more efficient to use these instead of snippets. Sparkup is only for vim, but zen coding is available for pretty much any editor under the sun.