Follow one of these links for economical ways to get to Scotland.  Hope you find them useful!

Easyjet The low cost airline.  Great value if you book on the internet and gets cheaper the earlier you book... Glasgow and Edinburgh.  Don't forget to checkout Easy rent a car if arriving in Glasgow!
Ryan Air The Irish connection linking up with Glasgow airport from a growing list of locations including many provincial UK airports. - prices start at £9. (Yes nine)
British Airways If money is no object then take a look at the B.A website.  Very good hourly service from Heathrow to both Glasgow and Edinburgh.
British Midland Some good prices can be had and British Midland offer a similar service to B.A.
Expedia Expedia can get you some goods deals.  This website is first class and scans all the major schedules to come up with the best prices.  You could save pounds off advertised fares.
BMI Baby Low cost budget airline
FlyBe Another low cost flight option.  Can now fly from Liverpool into Edinburgh and Glasgow