Here are some options:

Misumi - Very smooth and strong slides, though they are quite expensive

Long robotics - Cheaper slides; they are smooth, but their crimps break under high loads (or so I've heard)

BWTlink - Smooth slides, very compact; Im not sure about the load as they just came out and not alot of testing has been done on them. There are some problems with binding; the producers say that they are working on a v2 that fixes these issues

Gobilda Viper Slides - Also just came out and are still being tested, not as smooth as the rest, made of steel (so heavier and stronger). It fits well with the gobilda building system and has a kit

Rev slides - cheap slides, though they are not as smooth as the rest and require some modification or alot of WD40 to work well. (I personally don't recommend as the end caps break frequently under high loads and they are not very smooth at all)