1st things 1st ---- You need to decide what your trying to keep in the Nano and let the type of equipment be controlled by that decision. That goes for dimensions of tank also.
Examples:
SPS and Clams --- Long or flat tank w/ MH lighting
LPS and Softies --- most any tank will do (not to high though) and decent amount of PC's will sufice. Will also not give you heat issues like MH
A nice resonably priced setup that offer a high degree of flexibility would be:
Standard 10 gal tank.
CSL 96 watt Powerquad hood
300 GPH HOB filter
100 watt heater
optional
power head
all the necessary extras
That setup would allow you to keep a wide range of corals (most softies and LPS and some types of SPS). You could probably get the complete setup mail order for around $300 depending on your extras.