What's an interesting USB or network device for me to program?

My project, experix.sourceforge.net, is a command-line driven RPN style calculator, very generalized, intended for data acquisition, instrument control and data analysis. It has a 'usb' command that performs arbitrary control and bulk transfers. I am using it to operate a DAC-ADC device. I would like to add isochronous and interrupt transfers to experix's repertoire, but first I need to get a device that does those things and has programming information available. Can anybody recommend something? I also want to add capability to use ethernet-connected devices, via the kernel's socket interface. Any ideas on that?