I bought some casters off ebay that have been good.
And some other surplus heavy duty ones off craigslist.
Then recently I purchased two sets of casters from Woodcraft:
http://www.woodcraft.com/product/202...ed-4-pack.aspx
These are very nice and if Im doing something that I want to come out well and be able to 'level' on the feet - I do recommend them. (I did completely overload one and blew out the leveling foot, but thats nothing to do with the caster design and me just abusing it)