The Hewlett Packard HP-28C

Display: 4 line LCD (137 x 32 pixels) with graphics capability

Power: 3 N cells

Adv. Functions: Trig, hyperbolics, logs, stats, base conversions, unit conversions, solver, symbolic math (incl. calculus), matricies, vectors, complex math.

Memories: limited only by RAM

Programming: 2Kb RAM, programmable in RPL

Comments: Hobbled by 2Kb memory (quickly replaced with the 32Kb 28S model) but still quite powerfull. The clam-shell design never caught on, but the on-screen menus, graphics, and RPL language which first appeard in the 28C were featured in HP calculators right up until they stopped making them.