Methodic,
You might want to take a look at Warbirds. A free download is available at
http://www.iencentral.com/warbirds/index.shtml Warbirds was originally designed by many of the same guys that designed Aces High and has been around for 4 years or so. I think it is the most entertaiig sim out there, but the competition is getting stiffer.
You can fly Warbirds offline or against 1 other player for free, but in order to fly online you will pay between $1.50 and $2.00 an hour (you can buy time in vilume for a discount) -- a pretty stiff price for a lot of people. On the other hand, the sim has 70+ planes and variants to fly and there are many historical scenarios to participate in that are ten times as fun as the typical main arena furball fest.
WBs also has a totally new damage model in beta right now that really improves the sim.
Just my $0.02 -- I fly 'em both.
Absinthe, 352nd F.G.