This week AMD announced the $150 Radeon HD 4830 - get high-end performance on a budget.
The HD 4830 is a single-slot card (unlike the 4850 or 4870) runs at 575 MHz, and has a memory clock of 1,800MHz, 640 stream processors and 32 texture-management units. The hardware is capable of 740 GFlops. Memory is pegged at 512MB of GDDR3, and there doesn't seem to be a 1GB option for this card.
On the power front, this card sips rather than gulps, with a peak consumption of 110 Watts.
In terms of market, this card sits between the HD 4850 and the HD 4550.
This card will be picked up by all the usual vendors (ASUS, Sapphire Tech, Gigabyte ...).
Full spec here.