Personally, just thinking right off the top of my head the Awesome-8Q generates a lot of heat
That's only 31 Heat before Heat Sinks and Movement. An incredible amount for Introtech levels. The Stalker 3F runs a Heat tab of 44 before Movement.
However, the Warhawk/Masakari Prime pulls off 64 Heat before Movement. The Piranha can pull off 84 if it Rapid Fires all Machine Guns at full Rapid-Fire burst (really dangerous with its 10 Single Heat Sinks).
And we haven't really started getting in to units with Blazer Cannons or Heavy Lasers, either, like the Nova H with 10 Heavy Medium Lasers and 5 Jump.
I'm pretty sure the Tomahawk B generates somewhere in the neighborhood of 120. Unfortunately I can't remember off the top of my head exactly how many of each type of medium laser it mounts.
cERMLs do 5, cMPLs do 4, cERLLs do 12.
Swap out the ERs for Heavies, and you'd have a real stone burner on your hands. Too bad it doesn't have the crit space for all of that.
MegaMekLab and Solaris SkunkWerks keep a running heat load total while you're building a Mech, so pulling up a unit can tell you a lot.