On which Stack Exchange site can someone share code with others, similar to CodeToad?
There are three common methods for this, two appropriate for Stack Overflow, and one for Code Review:
Answer an existing question
Put it on Stack Overflow. The best place to put it is as an answer for an existing question. Search using the search box or google to see if there's a suitable question that your code would be a good answer for.
Convert it to a question
If you can't find a suitable existing question on Stack Overflow, you can ask the question for which your code would be a great answer, then submit the code as an answer. Let's assume your code is a QR code generator:
Then you answer it yourself:
Make sure to answer it quickly (in other words, compose the answer in another window so you can submit the question, then immediately submit the answer) so that other people don't spend a lot of time on it, or worse - close it. Although if it's closed as a duplicate, then you can simply post your answer to the question yours was marked a duplicate of.
Ask others to review it
Another place where it's suitable is http://Codereview.stackexchange.com - Post your code and ask others to critique it. I posted code to Stack Overflow long before Code Review existed in this manner, and it's been moved to codereview, so you can see an example of this here: CodeReview: Tiny Encryption Algorithm for arbitrary sized data
This isn't really appropriate for any of the Stack Exchange sites. If your code can help others solve a legitimate question that they have, then by all means, help them by answering their question. Otherwise, there are other sites for sharing code, such as CodeProject.
There is no Stack Exchange site for simply sharing code. Stack Exchange is a network for Q&A sites. If someone on www.stackoverflow.com has a question that you can answer, you can post appropriate and relevant parts of your code there.