Renss. Co. and W. Mass. riding!
You can also link up the Pittstown State Forest singletrack to Grafton for a long, more technical ride. MHCC does 3 weekly rides in Grafton/Pittstown (Wed, Fri, Sun), check the calendar at webmhcc.org (addy changed for some stupid reason). We do a lot of rides off the map also, so you can get to know the about 30 miles of trails out in G/P. I lead some rides with the club, so drop a line. I work in Renss Co so I ride a lot there. We also have a 4 mile technical time trail course on private land that I can show you.
Petersbugh Pass has a ton of trails and LOTS of climbing. The Mountain Goat in Williamstown, MA does a Tues ride, I believe.
Other riding: check out Lenox Mountain in Stockbridge, MA: tons of rocky singletrack with climbs. You can ride from Olivia's Overlook in Stockbridge to Kennedy Park in Lenox. The Arcadian shop sells maps and they do a Thursday ride out of the shop, as a trailhead's located at their back door. October Mountain (close to Lenox) has tons of hidden singletrack. I haven't done it, but I've heard it's a 4 mile climb on doubletrack then an almost 6 mile descent on singletrack.
Jiminy is a good local place to do downhilling. They have new trails being built every week with some north shore stuff., lots of jumps and drops up to 6 feet so far.When it's wet, though, that place is slimy as hell! Trail #4 is fun as hell, with fun jumps and flowy singletrack.They guys at the shop could also hook you up with local ride information like the trails in the Pittsfield State Forest (which connects to Jiminy Peak at the top of the mountain).