The Pentium III Xeon
Back in the good ole' days, you could always be assured of greater performance by getting your hands on the newest, most-expensive technology. Remember when hard drives had 100ms seek times and the 386 was twice as fast as a 286? Now of course, things are a little different (most say "complicated"). The Pentium II CPU wasn't architecturally faster than a PPro, but Intel was able to quickly push out higher-speeds, making the P2 a performance leader despite its lack of innovative engineering.
Now, the tide of computing is slowly shifting (as Intel would expect) towards their new Pentium III processor, buoyed not only by faster clock speeds, but also a massive Internet-targeted advertising campaign. Whether the P3 is a worthwhile upgrade certainly depends on where you stand, but barring any short-term surprises, it's probably what a lot of us will be running 6 months from now.
This brings us up to date with the Pentium III Xeon, which shares the same core changes as the Pentium III and maintains the robust server-ready features of the costy Xeon line. Even for the performance nut who needs the best for no other reason than the bragging rights, the disproportionately high cost of Xeon processors keep them from becoming spontaneous upgrades.