Despite what you're thinking, I don't just go swanning around at art parties and museums, I work like a dog at my studio and I have lots of opinions on art materials.
I use two brands of varnish for my paintings, in addition to the occasional use of retouch. The first is GamVar, a very fine product made by Gamblin. The package that I have comes with two glass jars. The first has varnish crystals and the second jar has liquid that dissolves and suspends the varnish crystals into a usable liquid varnish. The two jar method keeps the product fresher, in theory. I just went on the Gamblin site and it seems that GamVar is now being sold in bottles, so it looks like you might as well just get the single bottle after all and forget the mixing and shaking.
GamVar is glossy, but you can reduce the gloss by mixing it with Gamblin's Cold Wax medium. You can also make the varnish completely matte by applying the Cold Wax Medium and buffing your painting. I've done this and it works well also, especially on panels.
The company is well known for providing lots of good product information to artists and this is the link to its discussion of varnishes.
The varnish I've been using most recently is 'UVS Matte Varnish' made by Conservator's Products, available at this link. I like the matte quality of this varnish on my paintings. It comes with a little plastic bottle of UVA product and you add a drop or two according to directions as you mix up your varnish. The nice people at the company answer the phone if you have questions about anything, too, or if you have managed to lose the top of your squeeze bottle or tipped it over. The reason there's a rubber band around the can is because I attach the varnish directions to the can that way (it's a separate piece of paper).
The best way to apply your varnish is to pour it into some kind of china or porcelain saucer ( that's what I use) and use a little triangular soft white makeup sponge, available at your local pharmacy or megastore. These are perfect for putting on the right amount of varnish and you can also use them for applying powered charcoal or graphite or other dry media when you draw. They create a satisfying blockiness and mass when you draw this way and you can use the side or the edge of the sponge. Dual thank yous for this tip, the awesome artists, Sadie Valeri and Kate Stone.