Someone mentioned Macmillan and drmless ebooks earlier - just to clear that up; in the UK at least, Pan Macmillan are selling DRM-free ebooks
in multiple formats direct from their website.
If they're sold through other websites - Waterstones in the UK, say - they have DRM on them, so the way to go is buy direct from their own website at
www.panmacmillan.com (why they would have DRM on outside bookselling websites is a bit strange; I know that their head of digital publishing is very against DRM, so I can only assume that the bookseller sites such as Waterstones insist on the use of DRM, rather than the other way around).
According to a press release last year, the intention of UK Pan Macmillan is to publish all their subsequent black and white titles simultaneously in e-editions. This puts them ahead of most other publishers in my opinion (I'll have to declare some personal interest here since I'm published by them).