Rare among artists I like, I would actually recommend starting with a comprehensive Hits collection from Bowie. It'll give you a good overview, and make sure you hit the more popular points. After that, you can narrow it down to what speaks most to you -- my favourite period is the dark, mid-to-late-70s Berlin stuff (Low, Lodger, Heroes), but depending on my mood I like the pre-glam stuff (Hunky Dory, Space Oddity), the glam stuff (Ziggy should be in every collection, and I think Aladdin Sane is a better album...). I'm not fond of the 80s and Tin Machine stuff, but you might be...