Currently I have;
Maxis IKON for the front - super sticky tyre for dryer/dusty trails and by far the fastest - useless with event the slightest bit of mud - and show the damn tyre a thorn and you've a puncture.
Maxis ASPEN on the back - decent tyre actually - holds it's on in the dry and the wet AND it doesn't get clogged with mud.
But as others have said CONTI have some awesome tyres for summer/all year:
http://www.conti-tyres.co.uk/conticycle/mtb.shtml just keep in the XC / Trail section...
Race Kings are cool and fast, X-King remind me a great deal of the Maxis ASPENS & Mountain Kings are borderline for me if you want a faster tyre but are the muts nuts.