The Mesa 5i20 PCI card works well. It will handle 3 daughter boards. Use a 7i33TA PWM -> Analog board per 4 axes. And a 7i37TA for 8 outputs and 16 inputs. If you only need 4 axes, then you can add another 7i37TA for more I/O.
The 7i43 also works using the USB interface. It will only handle 2 daughter boards so it's a 4 axis only type of deal.
The main problem with the plugin at the moment is that it's a pain to install. You have to shoe horn a driver or two on. So a proper "setup" program needs to be done. I have one that works on my machine, but it's a developer machine. Installing it on a box stock OS always leads to an adventure.

But once installed, the plugin will drive motors quite well. Rigid tapping and everything, in theory...
And another thing... This is a servo only deal. No stepper interface. So you HAVE to know how to set up the PID values.
Steve