Also avoid getting the acids, carb cleaner, and gasket remover on anything other than what you're cleaning and dispose of used solvents, etc. in an environmentally responsible way. 

1. Normal wash: Good only for removing pure dirt and light oil. Use your favorite cleaner (I prefer Dawn dishwashing detergent over Simple Green or other "automotive" cleaners simply because a strong detergent gets the most of this type of crud off with the least effort.)
2. Pressure wash: Removes heavier dirt and oil but not any corrosion. Recommended only for whole engines. Avoid spraying at any exposed seals (like around the countershaft or tachometer pickoff, possibly the exhaust header seals, too). OK to hit normal gaskets.
3. Dishwasher: For individual pieces you get results similar to a pressure washing. Of course cleans the insides of pieces so be sure to blow air through passages to get out residual water. Do or don't tell your spouse about doing this depending on which path minimizes negative spousal reaction. (Mine was pretty skeptical - sniffed the dishes that were in with the parts to see if they smelled like oil.)
4. Sand blasting: Sand (silica or carborundum particle) blasting will seriously remove metal and leave an uncorroded, but pitted surface. Particles may become imbedded in aluminum if air velocity used is too great and/or the alloy is particularly soft. Use with incredible care if at all, especially on pieces with oil/water galleries. If you do, mask off all possible entrances carefully since any grit that gets in will be difficult to completely get out and any left in will likely destroy something in your engine.
5. Bead blasting: Small glass beads which shatter on impact clean off surface crud and leave the aluminum looking like it was tapped with a zillion microscopic ball peen hammers. Same warning on keeping grit out of passages.
6. Shell blasting: Ground up walnut (or other hard) nut shells are the gentlest of the three blasting methods. Removes crud and shallow corrosion and leaves the surface looking the most like it originally did. Note that the blasting methods are the only ones that will get corrosion off metal in the nooks and crannies.
7. Kerosene, paint thinner, gasoline, naphtha (in decreasing order of flammability and increasing order of volatility, I think): Use to remove oil, oily dirt, and tar. Use a wire brush or toothbrush to assist in getting off thick gunk. Does nothing for corrosion. Build/rent/buy a parts washer to speed cleaning of dissasembled pieces.
8. "Gunk" or equivalent: Gunk combines a petroleum-based solvent and a detergent in one can. Does a pretty good job on heavy dirt and light oil, nothing for corrosion. I think using a heavy detergent wash to remove heavy dirt, then a separate treatment of solvent to get heavy oil/tar off, and finally a second detergent wash works better than trying to do it all in one pass.
9. "Carb cleaner": is xylene and/or MEK (methyl ethyl ketone), i.e. an active, very volatile solvent. Good for getting the "varnish" and "paraffin" that form on the inside (and outside) of carburetors from old gasoline. Good as a general solvent, too.
10. WD-40: The solvent doesn't work as good on varnish as real carb cleaner, but of course WD-40 leaves the surface protected due to the oils in it. Use it immediately after you have de-crudded and brushed/blasted to keep surface shiny.
11. Hydrochloric acid: (available as muriatic acid). Takes off corrosion (not oily gunk), bubbling as it does so, but leaves the surface dark gray. Use a stainless steel wire "tooth" brush ($1 at your local car parts place) to expedite activity. Don't use it unless you really like this color. Avoid the fumes.
12. "Etching formula mag wheel cleaner": Available in a spray bottle and labeled "B" on the ABCDE specifier for automotive cleaning products, it contains phosphoric and hydrofluoric acids and bubbles when applied. Use a stainless steel wire "tooth" brush to expedite activity. Avoid the fumes. Leaves a dull light gray finish which can be lightened up by wiping with a paper towel/cloth immediately after brushing with the wire brush.
13. Gasket remover: Water-based liquid that softens fiber gaskets so they can be scraped off without damaging the machined surfaces. I mention it here because I found two uses for it: 1) it softens up the carbon and crud on the inside of the cylinder head, the ports, and the valve heads, which eased scraping those parts clean considerably. 2) It seems to soften/dissolve clear-coat (and other paint as well - be careful where you paint/spray this stuff!)
14. Wire brushes: You can get ones that fit in your drill and brush either circumferentially or radially and in different wire thicknesses. I recommend the softest wire for aluminum. Also get the wire "tooth" brush (and more than one) I mentioned above. Look in the welding section of your hardware store if you don't see them in the tools section. You can also mount a wire wheel on your grinder for small parts. Frankly, wire brushing (and blasting) are the only things I've found that clean off corrosion and leave the surface bright. It's a lot of work and can't get in the nooks and crannies but gives the best results. Clean surface with solvent first to keep brush from simply smearing the crud around.
15. Scotch-Brite pads: Available in about 6 by 9 inch sheets for a buck, they work well on clean, smooth aluminum to brighten it up, not effective for rough-finished aluminum.
16. Aluminum jelly: I tried this stuff years ago so don't remember exactly what it is (more acid-based stuff, I guess) and was disappointed in the results. But then perhaps that was when I still hoped for some magic method that didn't involve elbow grease.

Don't use steel wool on aluminum. Tiny bits of it will break off and stick in the aluminum. These then rust and you are left with "rusty aluminum 

Additional non-aluminum specific cleaners:

3M metal-stripper-wheel. This is a round plastic sponge, impregnated with abrasive grit, which you chuck into your electric drill. These remove tar, paint, rust from steel frames, tanks, panels. Probably a bit too abrasive for use on alloy, though. With one of these wheels, you can remove all the paint from, say, a gas tank without using any evil chemicals. It also removes surface rust, leaving you with bare metal covered with a network of fine scratches, ideal for paint adhesion. You then swab off your part with "metalprep", wash it off with water, dry it thoroughly, and paint away! That new paint will stick like glue! 

Get yourself a can of "Carburetor & small Parts Cleaner". This milky-white stuff will take the hide off an elephant. It'll take carbon off the tops of pistons. It'll clean your carbs good. Just don't put any non-metallic parts in it. You just dump your castings, jets, etc. into the can ( get the kind that comes with a dip basket ), and fish them out a half-hour or so later. Bright-squeaky-clean.

Another good carb cleaner is Berryman Chemtool. This stuff is about as poisonous and flammable as gasoline, but at least it's a good cleaner. Berryman's comes in a spray can, and its great fun to spray it on a grease-and-varnish encrusted carburetor; the stuff just liquefies and flows away. I personally use chemtool to clean carbs I don't want to take apart or off.

Spray it heavily with Gunk and leave it covered over night, then scrub with those plastic scratch pads. For the corrosion, Aluminum Jelly works good, but do it after you rinse the engine cleaner off.

In general, the rough cast cases clean up pretty well with some aluminum cleaner or carb cleaner solvents available at auto parts stores. Tide works OK, a brass bristle brush works really well. You don't want to polish the cases with buffing wheel, etc. Polished side covers, like most of the older British and Italian bikes had, are fine, but polishing the engine cases themselves will cause the engine to retain heat. If you do complete disassembly and have stubborn corrosion/need for resurfacing, a bead blaster with walnut shell grit works wonders. Finding someone to do this, however, is often a bit of a trick.