I can really only guess, obviously, but I would estimate that an AMD Athlon 64 x2 with 1GB of RAM and a Radeon 2900 pro running on a 720p display with AA off and low-medium settings is probably pretty close to current-gen consoles.
oh and in addition, games like uncharted or other exclusives like GoW3, etc, im sure if you were to see them coded for PC they would run horrible on comparible hardware like we have been listing because they were specifically designed for the console's hardware which is why it runs so well with nice graphics. This is why its hard to compare the hardware of a PC to any console hardware.
But, on multi-platform games what PCgamer said would seem about right
The RSX 'Reality Synthesizer' is a proprietary graphics processing unit (GPU) co-developed by Nvidia and Sony for the PlayStation 3 game console.
550 MHz on 90 nm process (shrunk to 65 nm in 2008 and to 40 nm in 2010)
Based on NV47 Chip previously based on the 7800 but with cut down features like lower memory bandwidth and only as many ROPs as the lower end 7600. (Nvidia GeForce 7800 Architecture)
300+ million transistors
Multi-way programmable parallel floating-point shader pipelines
Independent pixel/vertex shader architecture
24 parallel pixel-shader ALU pipes clocked @ 550 MHz
5 ALU operations per pipeline, per cycle (2 vector4, 2 scalar/dual/co-issue and fog ALU, 1 Texture ALU)
27 floating-point operations per pipeline, per cycle
8 parallel vertex pipelines @550 MHz
2 ALU operations per pipeline, per cycle (1 vector4 and 1 scalar, dual issue)
10 floating-point operations per pipeline, per cycle
Floating Point Operations: 400.4 Gigaflops (24 * 27 Flops * 550 + 8 * 10 Flops * 550)
74.8 billion shader operations per second (24 Pixel Shader Pipelines*5 ALUs*550 MHz) + (8 Vertex Shader Pipelines*2 ALUs*550 MHz)
24 texture filtering units (TF) and 8 vertex texture addressing units (TA)
24 filtered samples per clock
Maximum texel fillrate: 13.2 GigaTexels per second (24 textures * 550 MHz)
32 unfiltered texture samples per clock, ( 8 TA x 4 texture samples )
8 Render Output units / pixel rendering pipelines
Peak pixel fillrate (theoretical): 4.4 Gigapixel per second
Maximum Z sample rate: 8.8 GigaSamples per second (2 Z-samples * 8 ROPs * 550 MHz)
Maximum Dot product operations: 56 billion per second (combined with Cell CPU)
128-bit pixel precision offers rendering of scenes with High dynamic range rendering (HDR)
256 MB GDDR3 RAM at 700 MHz
128-bit memory bus width
22.4 GB/s read and write bandwidth
Cell FlexIO bus interface
20 GB/s read to the Cell and XDR memory
15 GB/s write to the Cell and XDR memory
Support for PSGL (OpenGL ES 1.1 + Nvidia Cg)
Support for S3TC texture compression 
So a Geforce 7600 is comparable to a PS3 gfx unit. And the Cell CPU is comparable to a Athlon 64 / Core 2 @ 3.2Ghz.
The Cell Broadband Engine—or Cell as it is more commonly known—is a microprocessor designed to bridge the gap between conventional desktop processors (such as the Athlon 64, and Core 2 families) and more specialized high-performance processors, such as the NVIDIA and ATI graphics-processors (GPUs).
Yea, I can't stand console quality (or lack thereof).
But tit for tat, consoles will always net better results then low-end PC's (despite being far less powerful) for the simple reason that developers can more easily develop games for a console, due to far less variables.