The most cutting edge would be a H&R 3.5" 20 gauge Ultra Slug Hunter.
It is a single shot, and has a bull barrel and is made specifically for making sabot slug shooting as accurate as we can get so far. There is a Tar Hunt bolt actions, but the price on those are crazy.
You can get a pump, which is what I have, in fact there is a new 870 barrel out there that is heavier than the standard, but not a bull barrel.
http://gunbroker.com/Auction/ViewIte...Item=115244268
http://www.hastingsammunition.com/
Also I have heard of really good results from Rem 1187's.
And this sight has a forum with people dedicated to shotgun sabot slug accuracy.
http://www.slugshooter.com/
You might also do a forum search and read on the past "arguments" on the sabot slugs, there are a few.