On the way would be Newick's in Dover Point. Always a solid choice for fried seafood and lobsters.
A little south but I always like Brown's in Seabrook.
The Oar House is a little more upscale and has been there forever.
This place in downtown Portsmouth was on some tv show for best sandwich with their crab grilled cheese. Never been myself but it looked damn good.
http://www.jumpinjays.com/