My browsing this last week turned up 3 vehicles that would look pretty cool in 40K. Have a look.
U.S. Marine Corps AAC (Assault Amphibious Vehicle)
As a recovering Guard player, this thing just screams 'Ogryn Transport' to me.
Indian Army 155mm Field Howitzer 77B (The Bofors Gun)
So let me get this straight... The Indian Army has a howitzer that's WAY cooler than any artillery piece in 40K? Wow. Self-propelled (but also towed), can turn in place like a Segway, and it has a cool ammo-loading arm? Wow.
Should be able to fire at least 3 shells at different trajectories so that they all land at once.
Indian goose-stepping is kind of entertaining too. ;)
The Czech BMP-M2 IFV
So it's basically the Chimera that GW should have come out with when they re-tooled their existing IG tanks 4 years ago.