I sometimes use lamp oil, that parradin stuff. Works really great. Also good for chain cleaning
And also use 'Sonax extreme wheel cleaner' (acid free), which works awesome as well. Is much easier to use when you are washing the bike anyway.
When you clean on a regular basis I guess you can keep the wheels clean using normal soap (e.g. for cars, never use that stuff you do the dishes with).
Since my MT will be my first bike I don't have much experience with motorcycle wheels yet.
I do detail cars as a hobby, so I have used a few different products on wheels.
I normally use P21s non-acid wheel cleaner for the regular wash, this will take fresh dirt easy and wont harm your wheel, brakes ect..
For old dirt, say if you haven't cleaned it for a week or two I use Bilt Hamber surfex HD, mixed in water at a ratio of 20% product and 80% water, this is also acid-free but at this mix its a bit tougher than the P21s.
For brake dust and other metal particles I use Bilt Hamber Korrosol, this is a clear fluid that turns pink in contact with contaminants so perfect for that sticking brake dust.
As protection I use Swissvax Autobahn wheel wax.
tar and bug remover ( for cars) or wax and grease remover (the stuff spray painters use to prep car paint) both are cheap and wont harm the finish on the wheels
I use Gunk ultra degreaser spray all over the bike, then hot soapy water, followed by a hosepipe. Halfords has it for a fiver, comes in a spray bottle.
You've got to get a good nylon brush to scrub the wheels if you want them really clean. They look OK after you've run a sponge round them, but when they dry they're still covered in crap.
[edit] ref WD40 - do you guys keep the bike inside or outside? Doesn't the smell get a bit over powering? Not that WD40 is an unpleasant smell, but it's s strong one. Not sure I'd want that in my garage all the time.