Ontario is great.
If you're looking for a direct flight, you might look at Long Beach. Jet Blue flies direct from Boston to LGB. When my wife and I make trips back east (NH), this is our preferred airline and our 2nd choice (after ONT), airport wise.
If I were flying into SoCal, I'd look at these airports, in this order:
ONT
LGB
PSP
SNA
LAX
For car rentals, we've had good luck price-wise with
http://www.foxrentacar.com/
