One trick that I've used a few times is to deposit unexpected bonanzas into my savings account rather than my checking account. This includes things like income tax refunds, rebates, travel reimbursements, etc. I also throw my loose change into a jar and deposit in into the savings account when it gets full.

The savings account is very accessible, but not so accessible that the money burns a hole in your pocket. You have to make a point to withdraw from the savings account -- either at the ATM or at the teller. It keeps the checking account a little leaner than it normally would be, and you spend a little less.