The access road to the standpipe on Greenleaf Mountain in Burlington affords a nice view of Boston. Also, the hill just south of the Mill Pond Reservoir, also in Burlington, has a nice view of Boston as well as the North Shore. I recall seeing the Danvers State Hospital from there too, using binoculars.
Didn't realize Burlington had these views. I will have to check it out. Also in Burlington, you can see it from Route 95. It's the middle Burlington exit (exit 33 I think) and there is an A and a B (Burlington one way, Winchester the other). In the middle of those the highway passes over an overpass, and if you look right (coming North from the mall) or left coming south, you get a great and fleeting view of the entire skyline.
Also you can see it on the mass pike just before the exit for 95. (or maybe while getting off that exit)
You can see it from the shore on the lynn/swampscott line (near nahant rotary, just north of it)
If you are on 93 north and you pass the 95 interchange, you can see it from the ramp of the next exit in Woburn (forget the name but it's the one with the Target, also it's kind of dangerous to look)
For hiking, there is Monadnock already mentioned, also Blue Hills has a tower and multiple closer peaks with great views, The Fells has a great view, and Noanet (in Dover I think) has a strange view of it from afar.
Ron, the hill crest on Route 2 has a park that runs parallel to it (behind the stone water tower at the park ave exit) and this park has absolutely ridiculous views of the city.
Ok that's it for now.