Man, oh man...
On some forums you would get about a shabbadabbazillion different answers. Here, hopefully you'll get a couple of good choices.
OK, I'll start:
I think most people put too much oil/lube/whatever on
Stains-Less steel blades. All types of steel
can stain, even that called stainless. But not usually just sitting there minding it's own business.
Carbon rich, lower Chromium steels are subject to peppering spots or even little spiderweb like spots, even during benign long term storage.
Alright already he says...answer the doggone question...
For me...
Carbon users get a mineral oil wipe, and a
drop in the pivot if they are folders, whenever I touch them up, (1-2 times a month), and don't get put away wet, unless I don't care what the patina looks like. Some of these I force a patina with vinegar (use the search if you're interested) to allow them to just be quickly wiped off after use, and to retard rust.
Carbon collectors get a wipe with a Tuf-Cloth (most gun shops) about once a year.
Stainless users and collectors just get normal reasonable knife care. A little mineral oil in the pivots after cleaning.
High speed...Low drag use...or saltwater use, is a different subject.
Mineral oil is available at any pharmacy (it's also a laxative

) for $1-2 a bottle.
Oh, WD-40 (Water Displacement...40th formula) is is a good thing to use if you need to clean up your knives (works great on tape, etc.), but I always blow it out with canned air. It is NOT a true rust inhibitor, like the Tuf-Cloth/Tuf-Glide products...
http://www.sentrysolutions.com/welcome.shtml
Not affiliated...yada yada yada. I just know these work from my own experience.
Whew!!!
Next batter.
Bill