Amphibians

Gray Tree Frog - Hyla versicolor
These guys can be found any color from dark gray to almost white. They do change to match their environment, so green is also a possibility.

Places I've seen them: Moose Hill in Sharon.

Wood Frog - Rana sylvatica
I've rarely spotted these anywhere near water.  Most of them are deep in the forest on trails.

Places I've seen them: Moose Hill in Sharon, Broadmoor in Natick.

Red-spotted Newt - Notophthalmus v. viridescens Adults are fully aquatic, juvies which I haven't seen can be found on land and are bright orange with the same spots as seen on the adult.

Places I've seen them: Garden in the Woods in Framingham.
Green Frog - Rana clamitans
I've found these mostly near water. More of the time they're actually in the water and have peeped and left before I get anywhere near them.

Places I've seen them: Moose Hill Sharon, Garden in the Woods in Framingham, Broad Meadow Brook in Worcester, Broadmoor in Natick.
Pickeral Frog - Rana palustris
I spot these guys in the grass near water early in the morning, or late in the evening. They are a little jumpy, but if you're slow enough they will hang around and let you photograph them.

Places I've seen them: Moose Hill in Sharon, Broadmoor in Natick, Ponkapoag Pond in Canton.
Baby Toads
Every year I find tiny toads at various locations depending on what time of the summer it is.  Invariably I find a few on the cape in July, with smaller ones around home in may and June. 

Places I've seen them:  Houghton's Pond in Milton, Cape Cod National Seashore in Provincetown, Wellfleet bay Audubon Sanctuary in Wellfleet.