We (Lollipuff, W13) released our entire application along with the short video [1]. I personally think that looking at a few sample applications is/was super helpful.

I also share SandersAK's opinion: just writing a YC application will force you to think about the "right things" for your business. It's a worthy exercise in its own right.

[1] https://www.lollipuff.com/blog/102/lollipuffs-ycombinator-ex...

EDIT: Awww! I just saw our old MVP screenshots on that blog post. Lollipuff has come a long way since then...