Army painter's Anti-shine (spraycan) gives good results for me ( but if you search on the forum you're sure to find different opinions)
As for brush on varnishes, go for Testors Dullcote (the square bottles, not the round ones) very matte effect and probably the favourite of a lot of people here.
I have also used valejo mat varnish in the past without complaints.
Recently I bought Matt clear from Gunze Sangyo and first tests seemes OK.