The HVL-F56AM was the flagship flash for Minolta/Sony from 2000 until 2008, at which time Sony came out with the HVL-F58AM. The HVL-F56AM is a feature-rich flash with plenty of custom functions, including modeling and multi-flash, a plug for an external battery pack, and a cable socket for Sony off-camera flash control.
For some reason this flash unit is now somewhat scarce, and seems to bring a high price at eBay and Amazon. Don’t pay too much, like over $300-$350, otherwise you can get the HVL-F58AM for a little more at a discount, or the HVL-F43AM for about the same.
This flash works well with Radiopoppers™ triggers, without the set-up hassle of the HVL-F42AM.