Calomine lotion usually works - or try one of the standard 'after-sun' preparations from the chemist. If you can stand it, use a hypoallergenic moistuiriser to prevent your skin drying any further.
Try putting some after sun lotion in the fridge before you embark on a sun tanning session, that way when you return all burnt, you will get immediate relief from said lotion.
If you can (like if you are not at work!) have a cool bath or shower to reduce the inflammation and take some of the heat out . THEN slather on your moisturiser - stuff with aloe vera in it is best.
or a bath with limeflowers anc cucumber in it, then aloe vera juice. Best of all apply factor 30 or higher suncream before going outdoors. This not only prevents sunburn but also staves off skin cancer.
I agree with the answers but the thing i found best is live yoghurt which has been left in the fridge for some time or at least a couple of hours, ie straight from supermarket fridge. Its thick and really works.