Techiton

ATI which merged with AMD 2 years back has recently launced their Radeon R700 series graphic card. The R700 follows a naming convention of 4XXX, a list of R700 graphic cards can be found here.
The two latest cards HD 4850 and HD 4870 offers a very high performance with a competitive price. The 4850 matches and often beats the performance of 9800 GTX while the 4870 matches that of GTX 280 with much lower prices.
A good review and comparison can be found at AnandTech: The Radeon HD 4850 & 4870: AMD Wins at $199 and $299

HD 4850 Specifications:
RAM Size: 512 MB GDDR3
Memory bus size: 256 bit
GPU frequency: 625 Mhz
Memory frequency: 1986 Mhz
Stream Processors: 800
Thai Price: 6,500 baht ($194)
Review: Tomshardware.com
Wiki: Radeon R700 Series

HD 4870 Specifications:
RAM Size: 512 MB GDDR5
Memory bus size: 256 bit
GPU frequency: 750 Mhz
Memory frequency: 3600 Mhz
Stream Processors: 800
Thai Price: 11,000 baht ($328)
Review: overclockersclub.com
Wiki: Radeon R700 Series