Whats your budget ? are you talking about a professional workstation class machine, or a home, DIY computer ?
If you're a professional, I'd look at a dual opteron from <A HREF="http://www.boxxtech.com/swf/index.asp" target="_new">BOXX </A> They make damn nice machines and offer top notch support. Have a look here: <A HREF="http://www.boxxtech.com/asp/cf_step2.asp?ModelInstanceID=281" target="_new">http://www.boxxtech.com/asp/cf_step2.asp?ModelInstanceID=281</A>
Why I picked an opteron ? cause the K8 is pretty good at maya, have a look here for some Athlon FX versus P4 Maya 5 benches:<A HREF="http://www.zdnet.de/enterprise/client/0,39023248,39115916-14,00.htm" target="_new">http://www.zdnet.de/enterprise/client/0,39023248,39115916-14,00.htm</A>. Keep in mind the Athlon FX is no different than a Opteron 148. Opteron typically scales a lot better than Xeon, and current xeons are a lot slower than the P4's tested, cause they are limited to 400/533 MHz fsb (compared to the 800 MHz versions in the benchmark).
If you are looking for something far cheaper, a P4C in the 2.8 GHz range might be worth looking at. The P4C's are currently a better value than Athlon XP's, especially for rendering. For something inbetween, but still single cpu, a Athlon 64 3200+ shouldnt be far from the Athlon FX/opteron 148 in rendering speed, and is quite affordable.
Hope this helps..
= The views stated herein are my personal views, and not necessarily the views of my wife. =