Hard to beat OJK for a fine natural smoke with jolt. Other than the obvious Gawith flakes, ropes, and mixtures known for turning some green. GL Pease Robusto can pack a bit of a kick. C&D Kelly's Coin is a good plain burley blend, similar in vein to 5 Brothers. Some find GL Pease, Haddos Delight quite strong. A fairly new blend, Peterson's Irish Flake has a nice kick.
Thanks for the suggestions. There are some names here that I've tried and some that I haven't. It may be time for me to venture a bit more into ropes and flakes as mostly I've been into ready rubbed. Cool thing about pipes - endless variations and choices to enjoy.
In addition to those already mentioned, I would add GLP's Cumberland.
Though I'm headed in the other direction, low nicotine but flavorful tobaccos, I've found the strength ratings on the Synjeco website to be helpful. They've rated the more common tobaccos on a strength scale from 1 to 10 with 10 being the strongest. They're website address is: Synjeco Tobacco Index
I'll put in another recommendation for Peterson Irish Flake. That stuff is killer in the nic dept (not to mention flavor)!
I also found Dunhill Three Year Matured VA to be very, very strong. In fact, I hated the stuff all around and was pleased to see that they don't make it anymore. BLEH!!! And I am not particularly wimpy about vitamin N, but this stuff was just bad all around. YMMV