IMO, GW's sealant works well, but like a lot of their stuff, is overpriced. Testor's Dullcote will give you a nice matte finish, for less money. Personally, I don't like a glossy finish on my models, I think it makes them look kind of fake. There's certain surfaces that look good glossy, like say, a monster's mouth, or something else you want to look like its glistening. For that, though, I find its best to use a paint on gloss varnish on the specific parts, while sealing the rest with matte.
Tekatana wrote:I nominate Viper!
I'd be happy too, but it looks like I got here a little late