I just buy my mediums with my paint, but here's the ones in my bucket:
Liquitex - Matte Medium, comes in a squeezy bottle
Windsor & Newton - Acrylic Matt Medium, comes in a jar (on the jar it says for a MORE fluid medium to use Acrylic Fluid Matt Medium)
Windsor & newton - Acrylic Fluid Gloss Medium, comes in a glass bottle (on the bottle it says to use Acrylic Gloss Medium for a LESS fluid medium)
I tend to use the Liquitex one most, only because it's in the squeeze bottle.
I work *very* liberally with my paints and mediums so the bottle makes it easier to throw more on the palette.