Go for one of the HD Hero cameras - my brother attaches his to his helmet or his board when kite surfing, or to his handlebars when cycling. Just a tiny bit bigger than a matchbox, and full HD video - really good kit!
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Rory
MkIIa, blue lit buttons, memory upgrade, 1Tb in Subaru Forester STi
MkII, 240Gb in Mark Lord dock
MkII, 80Gb SSD in dock