Ls W.
Google
THE place to get paper. One of the top stationers in the country, if you make work on paper it's practically a pilgrimage. The selection is astounding, the staff are very knowledgeable and take the time to narrow down your selection if you have a notion of what you need but nowhere to begin. If you have a particular budget, they can provide options to suit that too.
Despite dealing with them primarily over the phone for the last six years, it's still worth a visit. If you are printing south of the river, it's always worth the odd trip to Rumsey Rd. They are generous with samples, and it's an incredible luxury to be able to have someone take the time to show you first hand, so you can select by feel and sight rather than simply spec and take home some small pieces to try before you buy.
A truly professional art establishment, long may it continue.