There is not a lot of choice if you want 24mm equivalent on the M8, you have the Zeiss Distagon 18mm f4 ZM which is suppose to be stunning and the Leica 18mm f3.8 which is also suppose to be great but for a lot more money (another alternative is the Leica WATE).
Otherwise, you have the choice of going for a 21mm lens which will give you a 28mm equivalent on the M8. You have a lot of choice there:
CV Color Skopar 21/4, Zeiss Biogon 21/2.8. Zeiss C Biogon 21/4.5. Leica Elmarit 21/2.8, Leica Elmarit 21/2.8 ASPH, Leica Summilux 21/1.4, Leica Super-Angulon 21/3.4 or 21/4, Kobalux 21mm f2.8, Ricoh 21mm f3.5 and the Hexanon 21-35mm f3.5-4 (I am probably missing a few).
Check out the M-mount group on flickr to see sample photos with all those lenses: http://www.flickr.com/groups/m-mount/ (scroll down to the bottom of the page for links to the different brands).
Hi, if f-stop is not an issue, then the ZM C-Biogon 21mm f4.5 is the best wide money can buy. High resolving with no distortion, compact size and cheap
But there is something magical about the Elmarit 24mm ASPH...