It all depends on where and and on what you ride really. Some excellent suggestions above but they are more XC biased. The lighter tyres will get ripped to tatters before you know it if you are riding rougher rocky ground (I got sick of buying new Continentals and Schwalbes this summer).
My favourites are Kenda Bluegroove. Light enough and reasonably fast rolling for XC but grip well and resist damage on more aggressive terrain. Go for the Stick-E if you have a lot of wet rocks and roots locally, or the 2.3 DTC for a good all rounder that works just as well on hardpack and fireroad as it does on roots. Finally, If you have a lot of loose climbs on your routes you might want to try a Kenda Excavator on the back. Again a great tyre.