Have you set up a properly illuminated print viewing area? You need about 500 lux minimum illumination at the print surface to get a proper match to a monitor set to luminance of 80-100 cd/m2. Or as a crude but more brightly lit alternative, have you walked the dark prints outside in decent daylight to see if they still look too dark?
If yes to one or both of those questions posed above and the prints still seem too dark, then perhaps you've got a double profiling situation where the printer pipeline is making the conversion to the output color space more than just once. It happens in numerous cases where prints end up looking dark, but typically double profiling also makes the color balance look pretty bad as well.
Also, as Wayne noted, a trusted printer evaluation profile will help to sort out monitor calibration problems from printer/ink/media calibration problems. However, a trusted printer evaluation file, even when it looks good on the monitor and then printed on a correctly profiled printer/ink/media combination will also look too dark if your print viewing environment is not lit properly. Hence, it's important to understand that there are actually three major factors in getting good screen-to-print matching, i.e., properly calibrated monitor , properly profiled printer, and proper viewing illumination when examining the prints.
Lastly, are you choosing "printer manages color" or "Photoshop manages color" in PSCC? On a Mac and PSCC, "Photoshop manages color" should force the printer to "No color adjustment" mode and thus prevent double profiling, but if using printer manages color, you have to choose the "colorsync" option in the printer "color matching" menu. If that menu is on "Vendor matching" then the custom profile is not being invoked. Also, the Mac OS colorsync option was not working correctly, IMHO, on Mac OS7, and even in OS8 until the most recent Mac OS 10.8.5 update. So "PS manages colors" is the safer printing path for a number of reasons, IMHO.