Some excellent suggestions so far. I'd like to add Shingle Street and Benacre.
It depends what type of beach you're after. There are some magnificent broad sandy beaches in North Norfolk. Holkham is superb. A long sandy beach flanked by pine forests which has featured in a few films over the years. Brancaster is another favourite of mine. Another wide beach with the added bonus of a wartime shipwreck for added photographic interest. The ship was sunk there deliberately during WW2 to allow pilots some target practice before D-Day. To get up close you have to paddle across a river which runs across the beach when the tide is out. It can be done with extreme care and awareness of the tide.
The Suffolk beaches are almost all shingle if that's what you're after.
If you're prepared to move inland a bit try Maldon in Essex. It has a nice quay with old Thames barges moored up. You could also try the Butt and Oyster pub in Suffolk, just up-river from Felixstowe. It's a fine, very old pub with more Thames barges outside (I believe they are restored there).