I think building simple services where use JavaScript and databases will teach you a lot. I think you can figure out many ideas based simple info that you can spread to page.
It could be e.g. "Movie Collection", "Rating Service", "Dating Service", "Playlist Builder", "Simple Notebook", "Link Collection Page", "Sport Diary".... There is so much possibilities with simple data. And do not worry about if there already exist similar services only, so what, because you can do your own version! ;)
And most important of all is keep ball rolling, even with the most stupid ideas! :)
Ps. You don't even need to use databases at the beginning. Maybe just manual data. Just wanted pointing out that, because almost everything need somekind database. So it's great to handle it in someway. I just asked yesterday about "Easies database" and got great answers!