If you're looking for a classic Leica look, traditional ltm lenses are the way to go: Elmar, Summar, Summitar, Summaron.
If you want a compact mechanical body with modern optics, the Cosina Voigtlander 15mm, 21mm and 50mm's are unbeatable for price to performance. For 'fast', the Summitar f2 of the ltms and the Nokton f1.5 of the CVs are very nice and fairly inexpensive.
The Summitar is a beautiful lens wide open with gorgeous bokeh and pretty darn sharp stopped down and the 35mm f3.5 summaron w/ hood and is a fine, beautifully machined, tiny lens that makes negs I routinely enlarge to 11x14 and am satisfied with. You'll have fun either way.

Last idea: do a flickr search of images made with some of these lenses..theres lots of examples on there.
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