Are these any help? They might give you a few ideas.

http://www.xmission.com/~emailbox/folklore.htm

http://www.anythingleft-handed.co.uk/lefty_myths.html#1

http://www.gandolf.com/cornwall/supe...stitions.shtml

A few others:

It's bad luck to step on a crack in the pavement.
Lightening never strkes twice.
It's bad luck to annoy a bloke with a big sword.

How about a few magic related ones...

(From Pratchett) A night when all magic users must stay indoors.
Use of fire magic on a Friday can cause blisters and singed hair.

Maybe you could do area specific ones too, related to geography/topography and local history.

100 years ago the kings heir fell down a well on a Tuesday, so now people in the kingdom of XYZ beleive that using a well on a Tuesday brings bad luck.