There are four quadrant supplies out there - the Kepco BOP line is quite nice. They use noisy AC fans that are always on, however. Built like tanks. Not ideal for a lab setting. Lambda makes the BOSS line, but I believe they suffer from the same noise problem. Keithley makes sourcemeters which can sink and source current and are fairly quiet. Also very expensive - $2K+.
The BOSS line is no longer made but I have two NOS 20V 10A units. They are extremely noisy but very versatile. They can act as a high power op-amp up to about 20kHz. Makes a nice amplifier for a FG. My thread on mine here. My Keithley 2450 SMU is silent but only sources and sinks 1A.
I have used a Keithley source meter (2602B). Awesome specifications, but horrendous interface. Ugh. I think it really is designed to be used from a computer or with scripts, instead of as a normal bench instrument.
I personally own a HP 6825A. That's +-20V at +-2A. It does not have a fan, so it is dead silent. It can act as a four quadrant voltage source, or as an amplifier. It can do fixed gain or variable gain amplification. Very handy little device. I picked it up for about $100 on Ebay but it was very broken at the time. After a decent number of repairs it is now fully operational. It has an absolute current limit (ie you can set the magnitude of the current limit). This is both good and bad. For most people it is good. but I did like how on the Kepco BOP device I used to have you could have it act as a current amplifier rather than a voltage amplifier (so you'd set a current, not a current limit). So the 6825A is definitely missing some functionality IMHO. Even with that limitation, the 6825A is among my favorite pieces of equipment that I own.
They also made the 6826A (+-50V, +-1A) and 6827A (+-100V, +-0.5A). All three devices are pretty rare on Ebay, but you'll see a good deal occasionally...