It's funny, if I intentionally set out to rote memorise something, I almost always fail, but things that I use fairly regularly do seem to stick without my noticing. Off the top of my head I know:

my NI number
one of ccard numbers
about 10 years worth of passwords for various computer systems
my library card number (it's a long bastard) + PIN

I also used to know the account numbers + sort codes for my two Natwest accounts, before I closed them, but for some reason I've never memorised any of my current bank account numbers. Or my times-tables <g>

I understand very little about how brain works :/