For me, the obvious choice for multiple reasons is the Mitsubishi Sirius engine, specifically the 4G63/4G64, which are practically interchangeable in every sense.
The displacement of the 4G6 series ranges from 1.6L to 2.4L and covers both gasoline and diesel engines. The largest aftermarket displacement is 2.6L and has been done on multiple cars. It first appeared in 1979 in the Lancer, and is still produced to this day. If you're looking for one of the most influential I4's of all time, note that the 4G6 motor has appeared in almost every Mitsubishi model since the 80's, Hyundai and Kias, Dodges and Chryslers, as well as Eagle, Plymouth and a few Chinese brands. The current 4B11 in the Evo X, an all-aluminum I4 finding its roots in the 4G63, is a GEMA (Global Engine Manufacturing Alliance) motor, being the basis for many modern Chrysler and Hyundai motors. The 4G63 appeared in multiple sportscars: Evo I-IX, Eclipse, Talon, Laser, Conquest, Starion, Galant VR4, etc., winning the WRC four years in a row from 1996-1999.
That being said, let's talk about the versatility of these motors. There were two variants: Sirius I and Sirius II. The earlier Sirius I motors were found in early Evos and DSMs, and were mounted on the driver-side of the engine bay. The Sirius II, found in the later Evos and Eclipses, are mounted on the passenger side. The only known reliability issue was that late model Sirius I motors (7-bolts specifically) were prone to crankwalk. Generally, many Sirius I parts are interchangeable, same for Sirius II parts. For example, a DSM wanting a stroker 4G63 could pull the 100mm crank out of a 4G64, or a SOHC DSM could pull the head off either a 4G63 or DOHC 4G64. Kia and Hyundai really made these motors cheap by molding NA versions and using them in the Optima and Sonata, very common family cars. An Evo 8 head from a yard will run you $500+. I got an (almost) complete Sonata head for only $120! If an Evo 8 wanted a stroker they could pull 100mm crank, or the entire block, out of a Galant, Optima, Sonata, or Eclipse. Every exhaust manifold pattern was the same on every Sirius motor. This makes turbocharging any given motor very simple and easy (especially considering even many N/A variants came with low-compression). Transmissions for Sirius I engines, again, are interchangeable, meaning it's a bolt-on job to change a 2G Eclipse Spyder to AWD. Same for Sirius II, making it easy (though somewhat harder than the 2G) to convert a 3G Eclipse to AWD with minimal fabrication needed. Theoretically you could add MIVEC to any non-MIVEC Sirius II by dropping on a 4G69 SOHC MIVEC head or 4G63 DOHC MIVEC head.
Aftermarket support is where the 4G6 motor thrives. At least two companies make stroker kits, and parts are so commonplace that prices plummet. When you have your choice between several dozen different turbo manifolds of varying flange, material and mount, why pay top dollar? Let's talk about tuning.. Rather than set up a standalone or wire in a piggyback, most Mitsubishi models, specifically 4G63/4G64-equipped vehicles, are compatible with extremely cheap software (such as EvoScan and ECUflash, which are both aimed at Mitsubishi) that allows reasonably accurate tuning for one-fifth the price of a piggyback or one-tenth the price of a standalone. Every Evo, Eclipse, and DSM typically tunes this way unless they're aiming for very high numbers. Now back to parts, almost every part of the 4G63 has a wide array of aftermarket available. Cams? High lift. Harmonic dampener? Fluid. Bottom end internals? Forged. Timing belt? Kevlar. Intake manifolds? Too many to name. Turbo manifolds? WAY too many to name. Thermostats, head internals, mounts, wastegate springs, downpipes, piping, BOV's, MAF conversions.. Hell, they have aftermarket valve covers! LOL In terms of fuel there's dozens of brands of injectors ranging from 450cc all the way up to 2000cc. There's even a few double fuel pump kits for 4G63-equipped vehicles. Note that if you're building a Supra, for the same type of parts, you'd have to pay 3x as much. Supra manifolds start at well over a grand. If you've ever heard of AMS (the shop that makes the GT-R Alpha packages), they have built many crazy fast Evos. Just look up AMS Evo on YouTube.
Lastly, configurations of the engine. The 4G63 comes in every possible front-mounted drivetrain configuration: FF, FR, and AWD. It's easily possible to build a RWD 4G63 dragster or convert a FWD to AWD. Even if you don't wish to go with OEM parts, there's a guide to adapting a FF 4G63 to AWD. I've seen many various swaps both in person and online: FD RX7, several Civics, new edge Mustang, I mean come on, look at this Porsche swap:http://images.turbomagazine.com/images/ ... ne_bay.jpg
Here's the AMS 4G63 defeating a stroked RB26, SR20, LS7, F22 and VQ35 in Castrol's HP/L challenge (note it also defeated everything else in raw power except the twin turbo LS7 by a small margin):http://amsperformance.com/builds/castro ... -challenge
And if you're still not convinced, watch a 4G63-powered Eclipse run a 6-second 1/4 mile:https://www.youtube.com/watch?v=oHv_jKJVQ-Q
edit: There, I did a short presentation just like you asked..