The goodie is Yubnub. Possible uses are only limited to the number of websites over the web. I, for one, frequently use xe.com to convert money from one currency to another. However, the whole activity is quite cumbersome when you have to surf from one page to another just to get the required currency. With Yubnub as your default page, you no more need to do that. Just type "
xe -amount 1 -from AED -to PKR" in the search box and you can easily the converted amount!
A list of useful commands (aka Golden Eggs) is also available. The world is not short of useful ideas!