melee units (usu. hoppers or swordsmen, the latter are better for this)
heavy units (elephants of any kind or helipolii, cats are not advised, and only use one.)
ranged units (limit them only if u used ele archers)
Let this group mix as much as they will, they work very well as such. However, keep camels, hcav, or scythes (your speed units) flanking both sides, and note that you should not use cats.
for a 50-70 unit army, this works very efficiently against most simpler combos, both as outer defense and raiders. They are basically a slow-moving force that is hard to take down by any direct attack. On medit maps, sea support if possible makes things even more interesting.
For three groups, you have a force that can deal with most common strats. Against cats, simply hold back the main force, bring your eles, (hopefully archers) to take out the cat's defense, and bring in your flanking speed units.
Primarily, this strat chews up any massed unit, and makes life difficult for pairs, while working a reasonable budget.
The few times that I reach the point where I can use it online, it has been very effective. I look foreward to your input, and experience trying it out. (don't skimp on the melee units. they are an econ factor as well as numerical one.)
ps (eles take hits, melee increase firepower, archers can't be escaped if anyone attackes this force, but they need to be better mixed in than the other two. The formation is just an initial one for the sake or progressive copmosition, if you know what I mean.)
(this strat is most suited to civs with eles, even weak ones, but another unit will do, as long as you have four different ones. Three just don't seem to have the same effect.)
ok I'll shut up now. ------------------
Now keep yer eyes on the road and yer mind outta the gutter