What's an easy way to supply power to a breadboard without using batteries?
I have found these breadboard power supplies ($2.12 or so on ebay.com, shipped) very useful for the purpose described: 

 

Jumper-selected 3.3 and 5 Volt simultaneous outputs from wall-wart, USB or 9 Volt battery.

They have a convenient 2.1 mm barrel jack port on board, besides a power button and an indicator LED. You can choose to have 3.3 Volts on one of the power rail rows of the breadboard, and 5 Volts on the other, something I find especially useful.

As a fellow breadboard user, you might also find two of my answers to other questions on this site, of interest:


On "Good Quality Breadboards"
On "“Starter Kit for electronics” - What to buy?"