When applying for a job, it is important that you prove why YOU are the right one for the job they offer. And that you are motivated to get that job. What recruiters usually don't like are generic resumes, that have no relation to your (possible) future position.

So you should think "what kind of code will I likely have to write there?"

Is it some database-access? Is it some networking code? Is it some admin-script? ... Then pick some related functions from your home-project (and the corresponding test-cases), polish it and submit it. And don't forget to add some documentation ...

I cross my fingers for you! Rata

P.S.: don't forget to add a note that you have written your code "at home for your leisure" - and that it is not some code you have written for some other company ... and that you are not giving away their "secrets"

My background is in web application development, which typically means a script or even a framework application that accesses a database. That seems a little large for a code sample.

So prepare a tarball with the complete source code, and include one or two pretty isolated routines, maybe with a short description about the context they are called in.

I have a homegrown project that's an amusing distraction (it's an implementation of runoff that I did for a git flow presentation), but while all of the 16,000 tests pass, and perlcritic's OK with the source code, it's in mid-development, and not ready for prime time.

Polish a part of it and highlight it. No software is ever really ready for prime time, and no recruiter will look through enough code to make 16k tests pass.

See also: About 'Show me your Code'. I was particularly impressed by Your Mother's anecdote in response to that node:

Now for the anecdote. Couple years ago I had a contract that was making me insane when a job that was exactly what I wanted appeared on the boards. I wrote and CPAN'd a module related to the position as my cover letter. I got the job and with the highest salary I'd ever had by a lot.

You would not believe the number of utterly useless resumes that fall into one’s inbasket.   (And that somehow escape the clutches of the spam-filter ... one is constantly “tweaking” those rules, I’m afraid.)

Nevertheless, sometimes someone says something that causes you to pivot on your heels and take notice.   And so, in your third paragraph, I find two things that immediately attract my attention.  

1. ... git ... presentation ...   You know about git?   You presented?   When?   Where?   To how many people?
2. ... 16,000 tests ... perlcritic’s OK ...   “Okay, this is not a tyro.”

Any software engineer is, first and most, an engineer, and such a person’s true job description is to identify a problem, own it, and solve it ... all of this as a means to the end of creating robust, reliable, maintainable business software systems.   Therefore, what you want to do is to briefly describe how you did that.   Who relied upon you, and what references can you give to people who will affirm that you are the greatest thing since sliced bread?

As far as people are concerned, y'know ... you can train them, and they can learn.   If they’re disciplined and reliable and professional, and they don’t know a particular thing, just give ’em a book and a weekend and a $50 Starbucks card.   Everyone is constantly encountering things that they have never encountered before, and dealing with them, and delivering upon their promises.   So, when you are hiring, you are really looking for those qualities.   Reliability.   Resourcefulness.   Discipline.   Honor.

Make that shine.

As with everything in the job hunting process, put yourself in the position of the hiring manager. Imagine you're the person going over your code sample. What is most going to impress her that you are the best person for the job?

When I look at code samples, I'm expecting to see clean layout and indentation, with telling variables and comments that say not what the code does, but why it does it. Those are the basics.

Above that, I'd like to see something that relates to the problems that I have to solve. In your case, if the job you're applying for does a lot of web development, then show a web app. Better yet, show multiple web apps using different frameworks.

If you can somehow relate your code sample to the industry or specifics of the company, that's best at all. Applying to a book company? Then include code that looks up ISBNs online. Game company? Show something that tracks your Battle.net rankings. Etc etc.

No matter what you choose, make sure it is your best work. Don't include some crap code and say "Here's something I put together really quick, I know it's ugly."

When you are selling ... and you are ... it always behooves you to put yourself into the point-of-view of the person who will be buying.

You may want to find out if the code sample will be part of the interview, or merely part of a screening process. At least that way you may put together code that you would like to discuss versus code that would impress others when they review your code.

Also, maybe there's a portion of your homegrown project that is ready for prime time and easily discussed in an interview setting. If that's the case, then you could discuss the library and how it supports your current project.