Hard to beat PB Blaster - or, as it's known colloquially around here, "skunk piss". I've had decent luck with Liquid Wrench penetrating oil (the actual oil in the mini squeeze bottle) and good luck with Kroil for gun and knife related stuff.
Dealing with a lot of hot/cold cycling bolts in my job, just making a bolt really cold rarely causes it to break loose, if it's really stuck. It's typically a lot more common when dealing with different materials (like a magnesium plate with staked steel inserts, and high-strength alloy bolts), but a couple good hot/cold cycles is a lot more effective when dealing with similar metallurgy between the hardware and the bit the hardware is in, in my experience. Loctite stuff just looks gimmicky to me.