I've always just stuck to the Castrol Magnatec 5w30 A1 grade:

EuroCarParts were selling it for £17.49 the week before easter so I picked up 2 bottles then. Bargain if you ask me!
The only flaw with it is our cars hold over 4litres so a 4litre bottle isn't enough. I have an additional one in the shed however for adding the extra half a litre or so needed meaning I know I just need to buy 1 bottle to do 1 change.