PHP and MySQL work

I'm looking for ideas on what I can write in PHP and MySQL.  Thus far, I've written:

1) A comments system, that still gets hit by spam (but don't they all?).

2) An admin interface to upload documents, then create a record in a database for display elsewhere (along with categories and related articles/documents).

I just don't know - what do I *need* for functionality?  Maybe I'll look further into creating a RSS reader - I just don't know ...