Are there any mods out there that revamp the armor of the Imperial Legion in Oblivion to be more in line with the Romanesque styles seen in Morrowind and Oblivion? I've found a few retextures, but nothing that really stands out for me.

Amidst the many other things it adds http://tesalliance.org/forums/index.php?/files/file/1318-wac-waalx-animals-creatures/ does change the legion armors to look roman if you use the esp for it. Though since WAC adds so much more than just that I don't know if it would be what you're looking for.

Here are a few you can try. http://www.nexusmods.com/oblivion/mods/20354 comes as a replacer or standalone. http://www.nexusmods.com/oblivion/mods/41632, and http://www.nexusmods.com/oblivion/mods/43635.

http://www.nexusmods.com/oblivion/mods/28245 features a pretty close replica of the Morrowind Legion Armor.

I'm a big fan of WAC's legion armour. WAC is modular too, so you could technically only use the WAC.esm, legion.esp (whatever it's called) and rename the WAC.bsa so that it had the same name as the legion.esp. That way you would have WAC's Roman legionaires but none of the extra creatures etc that come with the full mod.

One thing to bear in mind though is that WAC's legion armor doesn't seem to have a female version, so you might have problems with mods that add female guards.

If you use HGEC and WAC this http://www.nexusmods.com/oblivion/mods/37594/?has a female version of WAC's legion armor.

The first one is just a retexture of the standard armour, and might not be what the OP is after. The second one is very Nice, but had texture issues when I tried it, and work seems to have stopped on it...

never really liked that one, TBH - the helmets look way off scale (too big), among other Things...

Personally, I'd love to see the Imperial armours from the Silgrad Tower mod made into a replacer for the default Oblivion armour, but I Guess that won't ever happen...

This one, while I admit to not having tried it myself (yet), seems to be the best: http://www.nexusmods.com/oblivion/mods/45024/

Looks like this one also re-References the default armout, so that any MODs that add Imperial legonnaires also get the New armour.