Levis Information?

[Rrrachel]

So I'm a little ignorant when it comes to jeans - small town upbringing or whatever, I'm only just beginning to understand these things like dry denim and selvedge.

Anyway, I am an owner of just one pair of Levis jeans, bought them off eBay as they are an unusual size for a womens pair (26W, 34L)its real trouble finding jeans which a) come in that size, aren't nasty cheap denim, and c) are an understated but interesting wash.

So, is there a comprehensive guide to Levis available somewhere? What do the numbers '501, 505, 507' mean? Is there a definitive list of cuts, washes and sizes available? How do you tell if they are fake or not? How do you tell good quality levis from bad quality ones?

Any information is appreciated. I'm off shopping in London on saturday and will be looking out for some vintage levis, so I'd better know what the hell I should be looking for!