Here's some specific information - Performance/Price wise.
I will gonna list only newest Intel processors, don't want to bother with Sandy anymore. So yeah, Ivy only. I don't know much about AMD Buldozers, but from what I've seen in zillion of test, they are quite slower in general. Even tho they can easily outmatch Intel in term of overclocking and maximum amount of GHZ you can get, and so the price, sadly however - it doesn't make their perfromance better. (Please, AMD fanboys, don't rage on me. It's just my humble opinion based on tests, not arguing here)
Intel Ivy's perf/price wise would be.
Intel Core i5 3570K - Best(in term of price/perf and possibility to overclock) Ivy's i5 out there, cost like ~210Euro in my region. Can be nicely overclocked up to 4+ghz and even more. Depends, if you're gonna use some non-boxed cooler or liquid CS. Imho, this one is the most price/performance efficient CPU you can get.
Intel Core i7 3770K - This one is simply best, but then again, price/performance ratio a little lower in my opinion then i5 3570 has. Cost nearly ~310Euro. Obviously you want to get this one to maximize your performance possibilities.
Not going to list anything else that cost like 500+ euro, because mainly it's not that useful as one may think it is. Both CPUs I've listed can be overclocked really high and provide you amazing performance for its price.
For those who wants good CPU and in the same time don't want to overclock anything, you should go for i5 3550/i5 3570 or i7 3770 without "K", because "K" means "unlocked" and stands for overclocking possibilities. You can save some euros that way.
As for AMD, I would like to see good alternatives, if someone can provide.