I have looked at offerings from MemoryMap and Anquet, but once you scale beyond a small area they become prohibitively expensive.
closed as not a real question by Shog9♦ Feb 1 '12 at 1:46
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You don't say what area specifically you're looking at, or what your budget is - but Anquet seems to do a number of electronic copies of standard OS maps for prices I wouldn't consider unreasonable here.
Of course, if you mean the whole of the UK / Europe then the cost will be high, but I don't think there's really much getting around that. It unfortunately seems to be the case that if you want this level of detail, you have to pay for it! Who knows, in the future perhaps prices will come down somewhat.