Expanding on the answers by [Tobias Kildetoft](https://meta.mathoverflow.net/a/957/9093) and [Joseph O'Rourke](https://meta.mathoverflow.net/a/949/9093).

There is some kind of automatic *Best Of*:

 * http://mathoverflow.net/?tab=month (the few on the top are almost always of general interest)
 * http://mathoverflow.net/?tab=week (to be more up-to-date and less selective; still, questions there are usually decent)

Also, based on comments there are some [StackApps](http://stackapps.com/), for example:

* http://stackapps.com/questions/4018/boso-best-of-stack-overflow

For more manual choice of questions (in the spirit of *Editor's Choice* or rather... *Mod's Choice*), I think the simplest way is to share links on G+ or Twitter (especially as sharing is already built-in).