All this is from memory, so you might need to double check some of it:
There was the MKS-100, which I think it was the S-10 in a rack, but might be wrong. It used 2.8" Quickdisks, like other similar units of the time.
Later, in the mid-90s, Roland released the JS-30, which was a DJ-style thing that looked like it should have been a poor-mans' MPC, but didn't quite cut it. Luckily they're pretty cheap now, so might be worth a try. They were originally 8-bit I believe, but were upgraded to 12 or 16 at some point from what I loosely remember.
There was also the MS-1, around the same time as the JS. It was a compact portable thing with very limited features, again probably pocket money nowadays. I seem to recall it using memory cards for storage, but it's been a while since I saw one.
The U series is still worth a pop I think. The U-110 was Roland's first rack ROMpler, and had 4 memory slots for cards with about twenty sounds on each. I've got about a dozen of them, they released 15 in all. When the U-220 came out, they improved the sound quality slightly and reduced the card slots to 2. A couple of the old cards were included in the 220's ROM. There was a keyboard version, the U-20. Editing is limited to evnelopes, LFO and such - basic modulation and mixing of the ROM waves. The interface is horrible, with about six buttons and a 2-line text display, but luckily there's so little you can manipulate, it hardly matters! I like the sound, its a little gritty and has character.
The W-30 is a nice unit. There's a sequencer on board, 8 outputs, and the sampling has a pleasant tone - not as clinical as the Akais. I don't much like Roland's mid-80s combo pitch-mod lever, but otherwise the thing is nice to play. Samples can be transferred pretty easily using disks if you have the right hardware - I have a few hundred NOS 3.5" 720kB disks, and a DOS-equipped laptop with floppy drive to cope with the library (which I downloaded from Sgroup).
There's some compatibility between them. The W-30 can read 550 files, and can convert 330/50 files. THe 760 is a different beast, and I believe the 770 was too.
The W-30's sequencer is compatible with MC sequencer files and Director-S files (which I think came for the 330/550, kind of a Fairlight thing going on). The MC-50 is also compatible with MC-500 files I believe, though I haven't tried it.
The old Roland library sounds are pretty good. I find sampling on the W-30 a bit awkward and convoluted, but it has a certain vibe, and like the Mirage, I keep it around because I'd instantly regret selling it! I've had a few Akai samplers in the past, and despite the popularity of those I never liked them very much in practice. I think the Rolands are keepers.
It'd be interesting to compare them to the Casio and Yamaha samplers of the 80s too.