You're probably not using all the datatypes available to you in PostgreSQL - there are actually quite a few. And that's not to say you should be using all of them, but it's always interesting to know what's out there, and to that end, Craig Kerstiens has written a list (complete with descriptions and/or warnings) of the PostgreSQL datatypes that you're probably not using:
- Range types
- Timestamp with Timezone
- Binary JSON
Again, some of these are cool little things you really ought to be using, and some can create unnecessary complications. Be sure to check out Kerstiens full article, then, to get all the descriptions and figure out what you're missing.