Monifieth is a pretty sleepy, almost-coastal little town on the River Tay, a few miles outside of Dundee. There isn't a massive amount going on, but it's a nice place to get a bit of peace and quiet.
The beach itself isn't one I would recommend for sunbathing or anything like that - far too cold, but some of the best beach runs I've ever had have been here - it's a great place to escape the city-bustle of Dundee. The sand is lovely and clean - it's usually quite solid too, and if running out towards the open sea, it starts to have a really secluded feeling to it - I loved all the washed up bits of old boats and other unidentifiable objects.
Also popular with kite surfers - they seem to be there as often as the wind allows.