Some days ago, forum user George posted a link in a relative forum thread for the Texas Instruments award winning WEBENCH® Designer. This excellent on-line tool will help circuit designers to select the proper chips (Texas Instruments of course). Here is the link (click).
The tool as an excellent and simple to use power supply design methodology. You can design your power supply according to specific design factors such as efficiency, footprint, cost, and of course the electrical characteristics and limits. Thank you George for this link!
After searching a little bit more for a cheap and small 3.3V and 5V SMPS, i came across an off-line version of the tool. The "Switchers Made Simple" can be downloaded from this link in a zip package. You can install this tool in your PC and design your SMPS power supply circuit with certain criteria and electrical characteristics. Very nice software!