I am assuming you want to do an SLI setup with the 8500GT's right? Don't bother. 8500GT's are weak cards and you would also have to buy a Nvidia board for SLI which is expensive given the mediocre performance of the 8500GT's.
I would buy the HD3650. It has plenty of memory and you can always add another one and crossfire them on a modern (P35, X38/48, etc.) motherboard.
Now my ultimate suggestion would be to buy a 9600GT if you want to SLI later on, or an HD3870 if you want to crossfire later on. Much more horsepower without breaking the bank.
Is it better to have 2 x 512MB Gainward BLISS 8500GT or just 1 Power Color 1GB HD3650.
Depends what you are trying to do... Well actually SLI is pretty stupid on lowend cards. The performance of both is usually lest than a single model higher card. The HD3650 would be the better of the choices.
What are you planning to do with these cards, that is the big question.