Well, judging from the one homoculus (whom I shall not spoil until after a lj-cut), that the anime showed, both of how they lived normally, and how they lived as a homoculus, I've come to the conlusion of....
All the homoculi are complete polar opposites of their original human forms.
So, lets start with the first three: Envy, Lust, and Gluttony.
Envy is an angry and jealous homoculus. We got to see a breif glimpse of it in the last dub episode aired: Created Humans. Envy expressed his deep resentment for by kicking Edward when he was down and commenting that he"carrys that bastard's blood in his veins".
So, I suppose when Envy was a human, before his creator did human transmutation to revive him from the dead, Envy must have been a very modest person, never holding grudges, and easy to forgive.
Some people say Envy is the homoculus of a failed attempt at trying to revive Honenheim's original body. I don't agree. I distinctly remember Hoho-papa or Dante talking about how the two had a son together, but he died... they tried to revive him with alchemy (I suppose with the Philosopher's stone), and somewhere in there the two tried to make themselves live forever as well. So, Envy is 'envious' towards Edward because they are half-brothers, and perhaps Envy is angry that Hoho-papa didn't create him to be a human, like he should have.
Lust! A very sensual woman, and uses her sexuality to get what she wants all the time. She prances around with lots of cleavage showing to boot.
So... her original human self must've been a very faithful woman who would never leave her boyfriend/fiance/husband.
We know later in the series that she was the homoculus created when Scar's brother tried to bring back his girlfriend/fiance/wife. Scar's brother's payment for creating Lust as well, was losing his manhood, (didn't anyone notice the blood dripping from his crotch?! I sure did!!!). The two must've been deeply in love for Scar's brother to consider going to any lengths to bringing her back...
Gluttony! They never tell Gluttony's past in the anime... he's just the creepy, childish fat guy who wants to eat everything and everyone.
So.... my thoughts are that the original Gluttony must've been a skinny and mature-minded person... (LOL that's almost impossible to comprehend! XD). No one knows who created Gluttony, or for what purpose. So this one is full of speculation...
Sorry sorry, back with more!! Using some ideas tossed in from replies
Greed! Well, he's just been introduced in the dub, though most of this shouldn't be spoilerific, rather, some 'no duhs' that one would associate with his character.
Greed, obviously is greedy. He even says it himself. He wants anything of value, and that usually falls into the money and women category... (you'll see him later on with a few 'trophy' females clinging onto him).
So, naturally assuming, I suspect that as a human, he would have been a very charitable, and if he was in a position of money, quite the philanthropist (rich dood who gives away money to anyone). Possibly also, he would have lived a simple life, with simplistic, and minimal material possessions...
Well, thanks for everyone that reminded me that Greed is directly connected to Dante. So yes, I'm going to assume that Greed must've been a child of hers, from a lover/husband she would have had after Hoho-papa left her, (they lived for 400 years or so, and Dante claimed she had been through countless of lovers, husbands, and whatever. Outsurviving them or just using them for her pleasure...) I don't believe Dante would have had more than a few kids with these lovers though... I think her only children must've been Envy, Greed, Pride, and possibly Gluttony.... I rant about Dante later...
Sloth! Well, as a homoculus she is very calm, collected, and dosen't exert herself too much. In the anime, most she does is tag along with Pride as the 'Furhur's Secretary'. Or, helping the other homoculi get around. But she dosen't go fighting too much. She lets everyone else go kick butt while she hangs back.
However, this Homoculus we know very well to be Trisha Elric. Poor single mother woman, worked herself to death raising Ed and Al. But it was all a labor of love, (*insert sappyness*).
Wrath! A very angry and wrathful child. Throws tantrums often, and sometimes those tantrums mess up the other Homoculi... Unlike the other homoculi who were nurtured to human-forms after their creation, or 'birth' by their creators, Wrath was sent to stay inside the gate for most of the time. I don't remember exactly how he got out, (did they explain that? I don't remember :x) And now runs around with the lost arm and leg that used to belong to Edward... (that child needs to definately get a sun tan).
Wrath is kinda different, he was an infant when he was transmuted by Izumi... and created a bit differently too. In the anime, Izumi created him by taking her dead baby's corpse and trying to bring him back to life... but he just mutated and crap. So Wrath can get around the 'body part of your old body will paralyize you' weakness.
My guess is, that if Wrath had lived and grown up, he would have been a very endearing, sweet boy who always obeys his mommy and would have been well disiplined (he'd have to be, Izumi is a psycho for disipline!)
But, Wrath shows us that if the Homoculi were influenced otherwise, they did not have to become evil beings.
Pride! Dante claims that she created him to be a homoculus who could age. So, he must've been created about 60 or so years back as a baby, and Dante, probably knowing enough about homoculi by then, figured out what to do to get him to age. As Furhur Bradley, he is kinda prideful. Always boasting, and in combat, very 'proud' in his fighting ability.
So, if Pride had been a normal human... he'd have been very humble and modest. Fuey (the geeky guy who works for Mustang) is possibly what Pride would have been if he was human: Shy, modest, geeky, and slightly clumsy.
And a thought about Dante:
Seeing as she created some of the homoculi, I have a feeling that she used the philsopher's stone and the body-swapping trick to her advantage: She'd create a homoculus for her own needs, using a body that was expendable, and after the ordeal was over, she'd just use the philsopher's stone to swap her soul over to a fresh body.... and all her body parts would be back.