Micro Four Thirds; Recommended Primes

I have an Olympus OM-D EM-5. Absolutely wonderful camera, though my only lens at the moment is the kit 12-50. While it's a great versatile lens, it is a slow lens, to say the least. So I'm after a prime, or two.

Here's my question: Which is your favourite prime lens and why?

I'm looking for something that is not too long - the Oly 45 is too tight for me. I shoot street and landscapes mainly. And I'm also looking for one that is faster than f/2.8 preferably.

I've heard great things about the Panasonic 20 1.7, though apparently it has slow focussing.
The PL 25mm is out of my budget for now - £300 is the most I'd spend on a single lens.

Finally, anyone out there use the Sigma 19mm or 30mm? Are they worth a shot?

Cheers!