When making purchases, be sure to use Canadian currency, debit cards or credit cards. Credit card companies actually do the currency conversions as they are billed to your statement.
Note: As of this writing - August 2010 - U.S. money is accepted at par throughout Niagara Falls, and converting to Canadian currency may yield less than par due to fees, so it may be more advisable to simply use US cash and avoid the conversion fees from banks and creditors.
There are a great many souvenir shops in Niagara Falls, especially in the Clifton Hill area and at the Maid of the Mist Marketplace at the foot of Clifton Hill. You'll find everything from the usual t-shirts and calendars to vials of Niagara Falls water.
Piccadilly Place Gifts
6022 stanley ave, (http://doubletree1.hilton...). gifts and souvenirs. five locations in town: at sheraton fallsview, sheraton on the falls, skyline inn, crowne plaza niagara, and doubletree resort lodge & spa fallsview.