Not counting Carmageddon, duh!

Flatout.

They should get Flatout 2 as well.

Apart from Flatout, I'd say Screamer 2.

Moto Racer 2. Yeah, I said it!

Seconded.

GOG could use more motorcycles.

I'd say Moto Racer.

Flatout 2. :P But it's not on GOG, what a shame! :(

To me best racing game on GOG is Moto Racer. The first one.

Generally, best value for money to most people will be Moto Racer 2 as it includes track editor.

I guess I will have to buy them some day, because many people recommend them :-D

I'm going with Powerslide, which is awesome. (I gather the Moto Racer games are good, but I've not played any of them.)

If you added combat to the criteria, Interstate '76 would be a no-brainer.

GOG needs the Moto Grand Prix games. Who owns those anyway?

THQ owned MotoGP licence until 07, after that Capcom. I think those games are in legal limbo, same way as CMR and TOCA.

I dare say you won't be disappointed. To me the first is nearly perfect racing game.

The second is not without flaws, most noticeable after a month of active playing is that AI racers tend to slow down even when that is not necessary. This usually happens at narrow pathways on dirt tracks, so if you want to produce a challenging championship (on hardest difficulty), there should be little to no motocross events. Speed bike racing is good; and motocross racing is not bad, just easy.

Take note that you will need a good keyboard or controller. Here response times are very important. This is fast racing.

Once before, after playing Moto Racer for a while, I felt I needed some fresh wind and obtained copies of Ultim@te Race Pro and Viper Racing. I still remember how it was to run those games after sticking with Moto Racer for a long time; basically, the speed in both was much too slow for me to enjoy.

Now go buy. Shoo! :)