Ffordes have a lot of stock, but their prices tend to be on the high side.
mxv.co.uk tend to have more reasonable prices, and a good selection.
Mr Cad (
www.mrcad.co.uk) has plenty of stock, but their grading is so wildly optimistic that I avoid them if I can.
Robert White are excellent to deal with in every way, but they don't carry a large used stock.
In Sweden, YFO and ProCenter have quite a lot of RB stuff, but the prices are just plain daft. But if you need something in a hurry, and they have what you want, they're good to deal with.
It's worth keeping an eye on the Swedish small ads site blocket.se. That's the only place I have seen real bargains for mainstream kit in recent years. There's a steady trickle of RB equipment mixed in with all the digicams and memory cards, some of it at very good prices.
There is also tradera.com, an eBay-owned, Sweden-only auction site. The LF stuff goes for stupid money, but MF is better.
But, and it's a big but, with the current low dollar it's very, very hard to beat KEH. Admittedly one return will wipe out most of your savings, but they grade very conservatively, and even with the tax and the shipping (and the tax on the shipping
you come out ahead.