I soak 'em in Ballistol.
Advantages:
* Cleans extremely well, while being fully "safe": it's non-toxic and food-safe and skin-contact safe, plus it does not harm other common materials on your knife: G10, wood, micarta, etc.
* Also lubes and provides corrosion protection.
Downsides? Some don't like the smell of ballistol. I actually like the smell (smells somewhat like the scent from an anise plant, reminds me of a salve that I used to smell in our horse barns when the vet came to our place), but my wife and kids don't like it. But either way, the smell dissipates within a couple of minutes on contact with air, once you dry the knife off.
The things I like about ballistol are that it is similar in purpose to WD40--it's a near universal lube, cleaner, and protectant. But unlike WD it's food-safe, and also unlike WD (especially on guns) Ballistol is a better type of lube for long-term use. Plus you can use it on an even wider variety of materials: leather (even boots, jackets, etc.), wood, plastics, rubber, metal, etc., and it has cool properties such as that it emulsifies with water (meaning that it mixes with water molecules without actually bonding to it, thus enabling the water to serve as a "carrier" for the ballistol that does not dilute its effectiveness). Black powder shooters actually make a mix of ballistol + water that they call "moose milk", and it's awesome for cleaning out their bores without causing rust.
There are a lot of things that work out there, and that I've used, but Ballistol has become my favorite because it's so widely useful while being non-harmful to people or the environment. And if you buy it bulk (by the gallon)--compared to most similar solvents like BreakFree CLP--you can get it at a pretty reasonably price-per-ounce, and a lot of popular retailers, gun shops, etc., carry it now (check out prices at this place, they are consistently competitive:
http://www.wisementrading.com/hunting/ballistol.htm).
