Finally got some time to take pics of my 1:18 (3-4inch) figures before work today. Descriptions from Left to Right.

Iron Man 2 Figures Mk6, FFR Gashapon Decade, SIC KT Blade, Star Wars Clone Trooper, G.I.Joe:ROC Turbo-Suit, G.I.Joe:ROC Duke, G.I.Joe (early 2000s) Neo-Viper, G.I.Joe (1980's) Cobra Trooper, BBI Elite Force Green Beret
Just a basic overview of the different 1:18 figures I've got. Well, roughly 1:18, anyway. The Superhero figs are on the left, soldier figs on the right. Now that I think of it, although Iron Man and the Riders are much taller
(With Blade, I think it's because of his helmet), it's not that far off considering Superheroes are supposed ot look taller than normal people.
BTW, the Elite Force series of figures were released by BBI toys back in the late 90's-early 2000's, but are no longer in production today. A shame, since they were pretty damn popular in the period that the G.I.Joe line was (relatively) quiet. Also, they were the first figure toyline (I think) that officially indicated they were 1:18 scale.

BBI Elite Force Green Beret, Captain Power figure, FFR Gashapon Decade, SIC KT Blade, Dead or Alive Gashapon Lei-Fang, DC Green Arrow, Marvel Iron Man, Iron Man 2 Figures Mk6, Jurrassic Park Figure.
The MArvel Iron Man and the Iron Man 2 Iron man figures are made by completely different manufacturers. The movie figures are made by Hasbro
(which is why they have similar design structure to Joe figures), I don't remember who makes the small Marvel figures. Thought I'd put them down here for comparison's sake.
The Jurrassic Park figure I got on a whim--5 points of articulation and nothing else--very reminiscent of late 70's-early 80's figures of this size. The Star Wars figures
ARE ALL EMP'S FAULT. Not a SW figure fan, but I got tempted to buy Clone Troopers because of him.
The Captain Power figure here, I've forgotten the name of, but was supposed to have been a villain for the (cancelled) next season of the show. Thus, the figure was released but long after the TV show's cancellation--which was too bad, since one of the new hero characters was supposed to be an ex-Navy SEAL.
Lei-Fang was released as a part of a series of Gashapons sometime back in 2004 or so, for Dead or Alive 3. The figure is pretty good, although you need to swap parts for some poses. There was a similar Gasha line for Tenjo Tenge which were around the same scale range. Both series seem to fit within 1:18 scale, since I occassionally pose them with my G.I.Joe figures.
Green Arrow is kind of obscured in the first shot, but here he is in the second. Sad, since I got him and Batman
(two of my favorite DC character--notice neither have innate superpowers), but was shocked that they were even shorter than most G.I. Joe figures I had.
BBI Elite Force Green Beret, G.I.Joe (1980's) Cobra Trooper, G.I. Joe (1990s) Ninja Force Storm Shadow, G.I.Joe (early 2000s) Neo-Viper, G.I.Joe:ROC Duke, Bravo TeamTank Commander
Initially just wanted to show comparisons of the four different generations of G.I. Joe Figures
(1980s, 1990's, and the two different 2000-era figs), but I ended up tossing in the 1;18 Elite Force and Bravo Team figures as well.
The Joe figures have superior posability, but ultimately the Elite Force and Bravo Team figures are far more accurate to real-life soldiers in terms of look and feel. There's a running gag amongst 1:6 scale collectors that almost none of Hasbro's Real American Hero Joe figures wear US Armed Forces uniforms.
Also: G.I. Joe figures from mid 1980's-early2000's had ridiculously outsized weapons
(they were closer to 1:12!), while the Bravo Team and Elite Force figures had them in the correct scale. Thankfully, all the Joe figures produced since The movie line have had most of their weapons resized to the proper scale--but not all.
I mentioned the Elite Force figures are no longer in production, but the Bravo Team figures
(You can get them at Kmart here in Australia) are similar, very accurately detailed and wearing current-era uniforms (Digital camo). There's also a 1:18 Bradley available for the figure--very cool but I don't have the space!
The only gripe I have is that the weapons that come with the figures tend to be machineguns (M240, M249), sniper rifles, or the M4 with M203--almost none of them carry a normal M4/M16, so I have to use extra gear from my Joe figures.