Mssimo: List of must have lenses:
Cheap:Panasonic 14mm f2.5Panasonic 20mm f1.7Olympus 45mm f1.8
Dream Kit:Olympus 12mm f2.0 or Panasonic 7-14mm f4Pani-Leica 25mm f1.4 or Voigtlander Nokton 25mm f/0.95Olympus 45mm f1.8and the new Olympus 75mm f1.8
All image stabilized (via body IS) and quite portable.
Share your own dream kits!
I have the Panasonic 14mm, Pani-Leica 25mm, Olympus 45mm, Olympus 9-18mm and Olympus 12-50mm. All of them are excellent lenses but they still can't touch my M42 Zeiss 50mm F1.4 when it comes to both image and build quality. The E-M5 combined with a $20 lens adaptor makes using M42 lenses easy and fun for my style of photography, probably because of the way that the EVF helps with the stop-down metering and manual focus.
The one thing that M42 lenses have highlighted is how plasticky and flimsy feeling all of my MFT lenses are, worst of which is the (otherwise excellent) Olympus 9-18mm. The cheap prices of M42 lenses means that my dream kit has changed a lot since I got my E-M5.