Does anyone make a PWM fan controller? Preferably one that controls 3-4 fans.

Most hardware shops offer at least a couple. Cheapest multi-ch unit I've seen is a 6-ch one by Logisys.

Why would you want one? PWM fans are fully compatible with normal 3-pin fan controllers, in case you didn't know, and will probably be comparably power/heat efficient if they don't use rheostats.

And if you're just out of places to plug in your fans, an aux-powered splitter cable will let you power and software-control an effectively unlimited number of fans from a single PWM header.

Why would you NOT want to control PWM fans via PWM?

Because you don't have enough PWM headers.

A PWM fan splitter like the Rosewill Model RCW-FPS-401 from Newegg is one solution to limited headers. Only the control signal is taken from the CPU header; all the fans on the chain are powered direct from the PSU. Is also inexpensive at around $4.

I'm surprised that there aren't more card-type controllers so that you have intelligent software control instead of manually diddling knobs to set fan speeds.

Then there's no rpm monitoring is there?

The way I've seen most of them work is that one fan on the splitter would still be connected to the PWM monitoring pin of the fan header, so there is monitoring of that fan. To some extent it assumes that all the fans you're using are the same (although they don't have to be) and would therefore all be running at the same speed.