In short, most music shop owners are clued up on the value of their stock, thanks to Discogs/ebay, so there's mainly tons of shit to sift through in the bargain bins in most shops. Those days of having the edge on the owner because they mainly specialise in other genres seems mostly gone in the shops I use. Even charity shops got clued up and pushed the prices up for the better tunes. Discogs then is the best bet for most people, but if crate diggin's in your blood then you can't resist the urge to have a delve at ever opportunity.
I still can't pass a record shop/charity shop if i'm on my own to see if there's any decent vinyl inside, but the chance of me finding something special is a lot rarer these days.
For stuff I really need though it's mainly Discogs for me these days, but i still check out ebay from time to time if I think a record's priced too dear on oggs, then usually find it's a lot dearer there (on ebay). Beware of buying from American sellers on oggs and ebay now though as I recently got screwed over by Parcelforce when they added a £13 processing fee on my order (plus other import charges) because they handled the parcel this side of the Atlantic.
I occasionally use Juno and other online shops for stuff if it's a new release too.
MVE in Notting Hill can throw up some good finds if you have the patience and decent knowledge of music and Vinyl Exchange used to be similar, but i haven't been there for a year or 2, so things might be different now. Generally speaking though, most of the cheesey old school music that charted on a big label can be picked up dirt cheap in the bins of MVE.
Cheers for the tips in Huddersfield
Last time I looked there all I could find was slim pickings in the charity shops.