I picked up a QX5fd on eBay for $75 to replace my trusty but limited QX21. I use it to record and play back synthesizer loops and as a MIDI clock source for my drum machine.
This box really kicks ass. It's got real-time and step-time note entry, 8 tracks, macros, looping capability, and a spiffy data entry wheel. The floppy drive really beats having to save sequences from the cassette port, too. The interface is totally straightforward, and will be instantly familiar to anyone who's used other QX series sequencers, and easy to learn for those who haven't.
If you can find one, don't hesitate to pick it up. It totally stands up to the ROLAND MC-300/500/50/50MkII in terms of features but is typically around half the cost because it doesn't say ROLAND on it.
A definite diamond in the rough for people like me who dig hardware sequencers...