The first Penryn based 45nm Core2 Duo processors have finally started to hit the open market. The best bargain of the bunch right now, is the humble E8400, which runs at 3.0GHz, with 6MB of shared L2 cache, for $189.00 at MicroCenter. Reports form the field indicate that it is quite easy to overclock this CPU up to the 4.0GHz range on air-cooling. Even at stock speed, it performs about 10% better than the older E6850 65nm Conroe (which also cost $100 more).
The entire 45nm line of dual and quad-core processors is listed here. You will need a newer motherboard and possible a BIOS update to be able to run this CPU.