OK, this is going to sound strange... I just tried out a module for the first time yesterday that I have owned for over a year and never turned on. I will explain later.
It's a Yamaha MU5. This thing is really small (the size of a VHS tape), easy to use, and sounds pretty darn good! Apparently they were like $400 new in the mid-90s. It's a 16-part GM sound module, with a very useful onboard mini (more like micro) keyboard on it. It can be battery operated and is SIMPLE SIMPLE SIMPLE. I downloaded the manual, but you really wouldn't need it.
I have been using my MacBook Pro as my sound source for a year and a half now, and though I still have a few drum modules around I never use them. I was setting up my brand-new LT for melodic use, and I just couldn't bring myself to go in the house, get the Mac, set all my stuff up, blah blah blah. I pulled out the MU5 (I had never even turned it on) and within seconds I was jammin' away on a pretty decent Vibes patch. The pianos are OK, Marimba kinda lame. Vibes are the best sound I have found in it, and some synths are good too.
The drum sounds are what you'd expect from General Midi... not editable in any way, but there are 8 kits to choose from, and they aren't horrible. This will now be my backup module for when the @#$%^& hits the fan.
And so why was this my best module purchase ever? 'Cuz I got it FREE when I bought a used TrapKat a couple years ago. I had always assumed I'd resell this thing later, and never got around to it. I'm glad I didn't! If you can find one dirt cheap, this would be a GREAT item to have in your gig bag just in case.