TTBT.
Alternatively, the XP-90 (not the XP-120) is good for its cost, size, and performance; it's not monsterous like the TTBT or the XP-120, so it's not too over spec for the HSF weight, and makes moving your case around, to LAN parties for instance, a lot more hassle-free. Besides, Athlon 64s run cool enough that you don't really need the very best HSF to keep them cool, even at the most extreme overclocking levels. For instance, my A64 3000+ Venice core E6 stepping processor gets to 2.7GHz at 1.7V (yeah, it's a lot of volts, but I was merely seeing how high it could go) and stays under 52C at full load with stock cooling. Overclocking figures for normal usage are: 2.6GHz 1.6V @ 47C full load. Even with stock cooling, these chips stay well under AMD's specification for the CPU temp. threshold.
Basically, what I'm trying to say is that I don't see the point in getting the very best HSF for your rig unless you're using a Pentium (I hear the Prescotts hit 60C at stock clock speeds). The Athlon 64s are just too good to warrant needing an amazing HSF, in my opinion.
Cheers!