John, the Sigma micro four-thirds lenses don't need adapters. But only two (the 19/2.8 and 30/2.8) are designed for micro four-thirds (the others are re-mounted SLR designs), and frankly, a lot of us are scratching our heads at why we should get excited about either one. They're both middle of the road focal lengths, already well covered, f/2.8, and not particularly pancake-ish.
My recommendation would be the
Panasonic 20mm f/1.7 pancake.
Beats the freaking pants off the Oly 17/2.8, and 1.3 stops faster making available light easier. And superb image quality.
Damn near universally recommended in micro 4/3 circles as a no-brainer purchase, unless you're nuts about bokeh and want something better than superb, don't mind paying for it, and are wiling to give up pancake compactness, in which case, go for the Oly/Leica
Summilux 25mm f/1.4.