Choosing Resonator for AtMega328P design
I've actually had to look into something similar (slightly different part) recently and decided to just use the internal RC oscillator.  It sounds like your issue is that you want to run the part at 3.3V so the 16 MHz oscillator (murata part traditionally seen on arduino boards) isn't an option (I believe that the highest frequency you can "safely" use the 328 @ 3.3V is 13.333 MHz -- see the graph in the datasheet -- you can linearly extrapolate).  If 8 MHz is what you want then I'd suggest just scrapping the external resonator and using the internal RC oscillator.  I believe that the part ships with fuse settings such that it defacto uses the internal RC with a clock divider of 8.  You'll need to reset that the clock divider fuses to 1, but you should be fine.  I found this link, which may be helpful.  You don't need to use the arduino stuff, but the link and downloads provide some clues as to how to do this easily.

http://arduino.cc/en/Tutorial/ArduinoToBreadboard