VTSC IG-88 and VOTC/Early Bird Chewbacca figures... To me, these two are probably the finest two basic figures in the modern line overall.
I'd have to give honorable mention to the EU Dark Trooper Phase 1, and the BAD Dark Trooper.
If I were to expand a bit and focus on the Empire, I'd go with the Spacetrooper and Black Pauldroned Sandtrooper (clean) as well... Both make very good representations of the basic Stormtrooper, and the Sandtrooper one even includes everything you could want for the trooper's field gear short of extra ranks. A close second and third for me would go to the VTSC Snowtrooper and the VTSC Biker Scout, as both are insanely accurate and detailed figures.
For the Rebel side of things, there isn't much, but I think the recent Pilot figures (Snowspeeder, A and B-Wingers, and X-Winger) are all great, as is the REbel Honor Guard which is not only obscure but very good. Then the last one I'd mention for the Rebs is maybe my favorite, in the Hoth Rebel Soldier from last year. It's fantastic, and such a shame we did not get the variation which was even better in terms of army building as it's generic.
From a purely aesthetic POV combined with "Wow that's a big figure", I'm always still impressed with Hermi Odle and Ephant Mon... Outstanding individual figures if a little limited in poseability.