I use Sci-MX whey protein powder, you can purchase this online or from some of the larger Tescos, be warned though its not cheap, but makes a quite nice shake, you can make it with water (like i do and its fine to drink) or add half and half skimmed milk to water to make a thicker shake, and comes in vanilla, chocolate and strawberry flavours.
Whatever you go for pic a product that has no sugar or fat and has the highest percentage protein you can find, the Sci-MX is 80% protein per 45g portion.
Invest in a plastic shaker as they smooth the lumps out.
Dont waste your money on soya protein drinks or power shakes, the soya products dont have the essential amino acids needed to absorb the protein.
My top tip - like anything else in life quality costs ! the cheaper products might seem good, but look carefully at the contents and quantaties before you spend out !