Okay, so this is a very sensitive subject, as a wrong cruising altitude can make you look like an idiot in the game, and/or crash you into someone headed straight for you..

I went onto the Zone to query real pilots/controllers.  What I got were some pretty wacked results..  This is what one pilot told me..

-Below FL180-
Odd thousands + 500
VFR-Easterly flight (hdg 000-89) - 3500 5500 7500 9500 11500 13500 15500 17500
Odd thousands
VFR-Easterly flight (hdg 090-179) - 3000 5000 7000 9000 11000 13000 15000 17000
Even thousands + 500
VFR-Westerly flight (hdg 180-269) - 4500 6500 8500 10500 12500 14500 16500
Even thousands
VFR-Westerly flight (hdg 270-359) - 4000 6000 8000 10000 12000 14000 16000
Odd thousands
IFR-Easterly flight (hdg 000-179) - 3000 5000 7000 9000 11000 13000 15000 17000
Even thousands
IFR-Westerly flight (hdg 180-359) - 4000 6000 8000 10000 12000 14000 16000

-Between FL180-FL290-
IFR ONLY
Odd thousands
Easterly flight (hdg 000-179) - FL190 FL210 FL230 FL250 FL270
Even thousands
Westerly flight (hdg 180-359) - FL180 FL200 FL220 FL240 FL260 FL280

-At FL290 and above-
IFR ONLY
Cruising altitudes at 4000' intervals, starting from FL290
Easterly flight (hdg 000-179) - FL290 FL330 FL370 FL410 FL450 FL490 FL530 FL570
Cruising altitudes at 5000' intervals, starting from FL300
Westerly flight (hdg 180-359) - FL300 FL350 FL400 FL450 FL500 FL550


Now, I don't know if these are infact correct, or if they're the altitudes for UK flight, but the help files here at Simviation tell me this:

Altitudes BELOW 18,000ft
VFR
Heading 000-179 (Easterly) -- ODD THOUSANDS + 500ft (3,500 5,500 9,500 etc etc)
Heading 180-359 (Westerly) -- EVEN THOUSANDS + 500ft (4,500 6,500 8,500 etc etc)

IFR
Heading 000-179 (Easterly) -- ODD THOUSANDS (3,000 5,000 7,000 etc etc)
Heading 180-359 (Westerly) -- EVEN THOUSANDS (6,000 8,000 10,000 etc etc)
** ALL FLIGHTS ABOVE fl180 (18,000ft) ARE IFR **

Between FL180-FL290
Heading 000-179 -- ODD FLIGHT LEVELS (FL190, FL230, etc etc)
Heading 180-359 -- EVEN FLIGHT LEVELS (FL180, FL220, etc etc)

At FL290 and Above
Heading 000-179 -- EVERY OTHER ODD FLIGHT LEVEL STARTING AT FL290 (FL290, FL330, etc etc)
Heading 180-359 -- EVERY OTHER ODD FLIGHT LEVEL STARTING AT FL310 (FL310, FL350, etc etc)


Now, I'm pretty sure that the altitudes listed here at Simviation are correct (for the United States), and my website also has the cruising altitudes within the United States that were checked over by trusted sources in the FAA/AOPA, and they match those at Simviation.. 

I ask you, WHICH IS CORRECT?

Note:  I'm on a quest to find which are the correct cruising altitudes, because some nut uploaded an erroneous text file to avsim.com containing cruising altitudes, and I wish to fix that.. BADLY...

I second that. 

Follow the Simviation set of rules, because that is what is instructed in the FAR's.

Ok, sorry Tim... getting kinda slow in my old age... and sometimes forget to check the forums for new stuff.