A list of what is unlocked by level anywhere?

[Enkidoh]

Really, it's not so much level that unlocks things, as more progression in the main storyline/class quests that unlocks content as you go. The only thing really level based that is unlocked upon attaining that level is rental chocobos and the chocoporter become useable upon gaining level 10. Also when your reach level 30 you get a Job upgrade for your class, and even that requires you to complete all your class quests from that class's guild first before the Job quest can be undertaken.

So yeah, it's not really level that you have to worry about for content, but making sure you're to date in the storyline and the quests given by your class's guild.