Hey, don't be totally fooled, while 939 is the better way to go and will provide increased perfomance, socket 754 is in no way horrible.
Now for the original question, the 90nm cores that AMD introduced in their Athlon proccesors came after socket 939 was released, and as everyone knows, 939 is now considered the replacement for the socket 754 and 940 socket 64 bit proccesors.
Because of this, no new 754 Athlon 64s will be introduced, so 90nm cores were never, and will never be introduced into 754 proccesors as they are technically "lost cause"(don't take that the wrong way, I simply mean AMD has moved on to the better choice, but 754 is still quite good).
So basically the 754 socket proccesors that you see on the market now are the only ones you will ever see, AMD has no plans to introduce any new 754 proccesors.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w