According to DanRadcliffe.de,  Matt Lewis (Neville) and Evanna Lynch (Luna) will be attending a Half-Blood Prince premiere next month in Zurich, Switzerland.  The date has not been announced yet but I will let you know when it has.

There is also a contest for fans to attend the special screening, with a competition offering two premiere tickets. The contest will be open until July 2nd; go here to enter!