I've done Greylock twice, and hiked it both times (once winter, once summer).
For an incredibly short and steep hike, take the old Thunderbolt ski trail up the E side of the mountain. I did this rather underprepared in winter, but imagine it would be quite easy in summer.
If you're looking for a longer hike, I'd definitely recommend the AT from Cheshire. A very nice hike with a few viewpoints along the way, and can be either a long dayhike (~16 mi) or an overnight.