I've shown this army in bits and peices in other threads but here's the whole enchilada. I'll have to do a bigger thing on pimping your guard but for tonight this will do.
More images at:
The army is still a work in progress, I started it in summer 2004 before going to Guyana and since I'm about to move back to the US who knows when it will be done.
To start with I wondered who says catachans have to look like this?

Couldn't they just be wearing tight long sleeve shirts? And for that matter who says that's a tee shirt, couldn't it be body armor? And what about those faces? If they wore full masks I'd never need to worry about painting faces again!
I've done crazy IG before, Zombies, Zombie armored company, Inquisition and using EM4s plastics figures but I have never really tried a 'realistic' army. And you never know when you'll need a fifth IG army.
Since I would be replacing GW lasguns with real world weapons it had to be Catachans, Cadians have the left hand attached to the gun making weapon swaps nearly impossible.
Kits like this would provide the guns, they're a bit smaller than GW weapons (which is funny since 1/35 scale is about double 28mm scale but that's GW for you) but are pretty clearly lasguns/autoguns.

Available at:
http://modelwarehouse.safeshopper.com/10/cat10.htm?408
Specifically at:
http://www.modelwarehouse.biz/85/cat85.htm?976
Unfortunately my favorite kit, the MP5 collection is OOP, I got the last 5 from Model Warehouse but M16s and AK47s are just as doable.
So here we go!
Test model, a GW shotgun, green stuff and a US WWII helmet.

And some other early successes

I mused using real world weapons as GW heavy and special weapons. SAWs and LMGs as plasma, TOW missles as las cannons, LAW rockets as meltas... I might still do it, mybe even make extra models for the realistic and GW versions of the army and let my opponent pick. Yeah. Sure. Why not? Maybe someday...
But for now I'm sticking to GW guns. The Raptor weapon sprue provides plasma and meltas that are the perfect size for my SWAT teams. Using them with the blunderbuss arms (rolled up sleeves) from the Empire militia sprue worked very well.

Heavy weapons are mostly from the now defunct Warzone line, they had seperate packs of heavy weapons that look real world enough for my guys. The Lascannon on the right is a Chaos Havok one, I was about to pick up a bunch more till I saw GW wants $5 each for them. @##$$ that!

Submachine squads are the meat of the army, darn they look cool if I do say so myself.

They will be getting cameo stripes one of these days...

WWII German helmets, no masks this time just to see how they look

With the urban war theme Hell Hounds were a natural choice. I can even tell myself it's shooting a water cannon.

Besides the guns most of the kits I used are available from:
http://www.towerhobbies.com/listings/cat-cat-s.html
In this category
http://www2.towerhobbies.com/cgi-bin/wti0093p?&C=SJB
Italiari, Tamiya and Dragon are my standbys. Here are some vital kits for any IG pimping project
Italitari 1/35 WWII accessories, ammo boxes, guns, crates, lots of useful bitz
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXR256&P=0
Tamiya modern US accessories, modern packs and bitz, many backpacks end up too large for IG but there are enough useful ones to justify buying it.
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFRZ4&P=0
And finally the #1 pick, Tamiya WWII German and US accessories, each one has 5 or 6 helmets (which fit IG if you trim their heads) and other bitz for just $4.50 each.
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXGV36&P=0
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXGV37&P=0