Here's my list mostly from the area around the canal
The Seafood Shanty on the Scenic Hwy (Rt 6 between the bridges)
East Wind Lobster in Buzzards Bay (just off the old Bourne Bridge Rotary)
The Lobster Trap Shore Road Bourne. Unfortunately, this place has been "discovered" and is expensive and hard to get into. They went from a porch next to a kitchen to valet parking and police directing traffic.
Right on the Bourne cape side rotary is the lighthouse where you can get a lobster roll for lunch. This is where we get out lobsters and steamers.
There's a new place (haven't been yet) on Sandwich Harbor on the canal that's reported to be good food, but difficult to get into.
Other places on the Cape I've been to Baxter's in Hyannis, Kreme 'n Kone in Chatham and Dennis. Ok but ridiculously expensive.
Seafood Sam's is overrated.
If you make it out as far as P'town, just about anywhere there is great.