Athlon 64 roadmap
AnandTech: Socket M2 Processor Roadmap; FX-62 and Athlon 64 X2 5200+. Since I've torqued either my CPU or my motherboard. It is nice to know that there aren't any big upgrades on the horizon. There is a new socket system from AMD due 2QCal2006, but that is a while from now. In the mean time, both Intel and AMD are just lowering prices.
For instance, the Athlon X2 3800+ (codenamed Manchester based on Venice)I bought last month for $400 is now about $320 from Newegg. These are the most popular because they run at 2.0GHz but can easily overclock to 2.4GHz and even to 2.6GHz with the right cooling. Good "reviews":http://anandtech.com/news/shownews.aspx?i=24664 on the web for the Venice based dual cores that run with 2x512MB caches. There is a newer version called the Toledo with 2x1MB caches that are still expensive at $400 but which run about 10% faster. So the 2.2GHz part is rated at 4400+ vs. the Manchester part at 4200+.
When I had my X2 system working, it wasn't really faster for games, but it was way more responsive when doing browsing, etc.
For more budget performance if there is one. The well single core chips are codenamed Venice and launched in April. They feature about a 16% improvement in nominal clock speed, so you should see real speeds of 2.8GHz now. The best priced are the Athlon 64 3500+ at about $180 righ tnow.