The free VATCalc is a fully configurable, general purpose sales tax (e.g. VAT) calculator.
Enter the cost of an item without tax to find the true cost at various tax rates or enter the cost at the basic rate to calculate the net cost and the cost at the other rates. You can then email a formatted copy of the results for future reference so you don't have to write anything down.
The list of supported rates is fully configurable letting you customise VATCalc to show exactly the information you need.