We will be in Boston mid- May and love theater, music, etc. May seems to be thin on these activities (not high season). Can anyone recommend good local theater that might still have shows going? I like to plan in advance.

best to google the theater schedule
www.boston.com
the arts and entertainment calendar is a good start

Also if you like other than larger name shows, make sure to check out the Boston Center for the Arts, Lyric Stage ART/ Huntington Theater as well as Wang Center and Cutler Emerson Majestic -

Always showing are the Blue Man Group, Shear Madness.

also citylinks.com and theatermania.com

Oh, also check out what is happening at the musuems.
Sometimes fabulous music !
The Isabella Stewart Gardener Museum has wonderful evening performances -
as does the MFA (and a new restaurant Bravo if you want to combine it with some museum, dinner and show)
ICA (although quite different selections than the other museums. -

those specific calendars should be up on their web pages

Try www.broadwayacrossamerica.com. There are some shows at the Boston Opera House in May.

check out www.artsboston.org and improvasylum.com

Take a look at www.showofthemonthclub.com

New shows have been added for May. You don't need to join to purchase tickets directly from the venues.