Henry said:
Mana points go back as far as Spell points in Tunnels and Trolls, near as I can tell, in the 1970's. Feats have their roots in GURPS advantages (I've heard it rumored that some of the 3E designers were inspired for feats in Fallout's Perks system, which was a direct offshoot of GURPS, since fallout was supposed to be a GURPS game originally). The Difficulty Class system came from Ars Magica, near as anyone can figure out. And most other RPG innovations that I've heard of came were first fleshed out in either fiction or other RPGs first rather than from computer games.
I will concede the existence of MP-style systems before Dragon Quest, then. Since you didn't mention per-encounter balancing, I think I will take it that you accept videogames may have been an inspiration for the idea.
What do you mean by things being "fleshed out by fiction"? Rules do not exist in written fiction (and any good writer will tell you that any rule described in a text only exists to be broken).
I've decided you're right -- I clearly don't play enough video games, because I've never heard of any of those, prior to just now.

I'm curious which ones in your opinion would have some ideas or mechanics that would really benefit any given RPG (not just D&D).
Hmm... this will take some thought...
I like Aterlier Iris 2's Mana Syntehsis concept, which lets people called Alchemists create an item through difficult, traditional alchemical means, and then make an potentially infinite number of copies of that item, even in the middle of battle, by using energy taken from deconstructing local matter.
The idea of Avatars from the .hack//G.U. videogames, is something so cool that I
will make a D&D campaign based on the idea sooner or later. The .hack series is the odd concept of a single player game in which you control a guy playing in an MMORPG that has seemingly supernatural things occuring inside of it. An fascinating way of using a videogame to talk about videogame culture, really. Anyways, the "Avatars" are powerful super-AIs who personify themselves as glowing giants that are paired up with each of the major characters, allowing them to break the rules of the MMORPG that they play and do things that are not permitted by the game program. One major ability is Data Drain, the ability to absorb the data of a target, rewriting it completly and turning it into a useable item or piece of equipment.
The main premise of Wild ARMs is a wierd hybrid of Wild West gunslinging, traditional Fantasy settings, and a few nanotech demons and giant mechanical golems. The Force gauge, Force abilities, Wild ARMs 2/3 style force-dependant spells (based on having a minimum on the gauge, rather than consuming the guage), Mediums, and the HEX system... There are a lot of things here that are fairly unique. Maybe I'll get into this one later.
While the main gimmick of Shadow Hearts, the Judgement Ring, is wholly useless to tabletop games, the way it uses Sanity as a per-encounter resource that, in addition to providing a time-limit on a character's ability to fight, can be used up to allow powerful per-encounter abilities (like Yuri's demon transformations) is a great way to balance Lovecraftian horror with a long-running, fight against the horrors and maybe win kind of campaign.
Chrono Trigger's Dual Tech/Triple Tech system is very interesting because in that game an individual character's abilities are just building blocks for the much more powerful combination attacks two or more characters can use in tandem. A warrior's special sword attack and a mage's fire spell can be combined into a far more powerful hybrid attack. An Ice spell and a Fire spell cast by two mages can be forced together and trigger an Antipode/Reaction attack that results in a Shadow element spell, something neither mage can use on her own.
Similarly, in Breath of Fire 4, characters can chain together magical attacks, so that using a spell of a certain elemental after an elemental attack will lead to a much more powerful mixed element attack. The Dragon Gene system of Breath of Fire 3 and the even more amazing D-Dive/D-Counter systems of Breath of Fire: Dragon Quarter deserve mention as well. The latter is the only good mechanic I have ever seen for a character who is given infinite power, but is doomed to inevitably die from having that power.
Ar Tonelico is a really interesting system as a whole, but I think the two best parts are the use of MP as a limiter on duration and maximum power of magic, rather than number of uses of magic, and the way it lets the caster choose the power of a spell by just letting it charge and gather strength over time. Also, the way it uses buffs, as short term and
very powerful (a
basic buff will give characters immunity to electricity, gives them enough bonus electricty damage to double the damage output of normal attacks, and slowly heals them, however it requires constant concentration and the caster's MP will run out only after a few turns). Because MP is constantly drained while casting magic, and regenerates pretty much instantly when not casting magic, it is a very different kind of resource than normal (interesting, a kind of regenerating spell-slot system is combined with this MP system).
I think this is enough before this post gets too big.