I only buy French red wine; any of the Sainsbury's "house" ones are OK. They vary a bit from bottle to bottle but the Corbieres and Cotes du Rhone have been good. You can pay 3x the price and get worse, anyway.
I like German Rieslings, which were also cheap because of the relatively low alcohol content (most are under 10%). However, German wine been squeezed out of the UK market by New World branded wines with of unknown quality (no QbA or AOC here) and it's almost impossible to find a Bereich Bernkastel or even a Piesporter Michelsberg in the supermarket these days.