EBuyer seems to be cheaper than everywhere else in general. On top of which they have a free shipping option. I just got a Kingmax 512MB MMC from EBuyer for £32.49 (delivered within a week for free) as my Viking 64MB MMC is dying (getting lots of errors). Looking at other posts, Zaurus users only seem to have good experiences with Kingmax branded cards, so I'll see how well mine works next week.
And to think, just over two years ago I paid even more than that for the 64MB MMC.
EDIT: Got it today. They despatched it when they said they would (yesterday) and the postie dropped it off today. Am very impressed. I get 1.5MB/s read AND write speeds, which is easily enough for video too.