Can't really comment on any other supermarket than Tesco, but generally speaking the following tesco value products are decent enough:

- market value veg
- chopped tomatoes
- kidney beans
- frozen peas
- rip-off Penguin bars (basically just taste like Penguins... look a bit moody though)
- ready salted crisps (pack sizes are a bit stingey but they taste fine)
- kettle (it boils water and keeps the scummy bits out. what more do you want?)

great thread. please add to this list.