There's information on the SONISPHERE festival - (check here) about dates in Sofia, Bulgaria- June 22nd -23rd.

It still not clear which bands will participate in the event, although the buzz around the 2010 event in Knebworth, UK started a couple of days ago when SONISPHEREВ  and IRON MAIDEN web sites prepared us for major announcements to be made today at 6 p.m. GMT.

And while there's no much information about the Bulgarian SONISPHERE, in Poland, on June 16th things are already shaping:

METALLICA
SLAYER
ANTHRAX
MASTODON
BEHEMOTH