Despite all current shortages: Intel's Pentium III is still the most popular processor. Meanwhile, AMD's Athlon is steadily stealing little peaces of the gigantic cake. With the introduction of the Thunderbird and Spitfire cores, I expect Pentium III prices to drop considerably.
If you are out for a Pentium III processor: It's very easy to spend a lot of money now. Considering your real demands are more important than ever. In my eyes, the 100 MHz models are really old-fashioned today, as they cannot hold up to their 133 MHz brothers. Most motherboards using the VIA Apollo Pro 133A chipset can be configured very flexible regarding the bus speed issue. A 133 MHz CPU using 100 MHz SDRAM is no problem. You can also run a 100 MHz FSB processor while using PC133 memory.
Overclockers should go for the Pentium III models 500E, 533E, 550E, 600E, 600EB, 667EB or 733EB. The higher the clock speed, the bigger the risk that overclocking won't work properly. As long as Intel is having difficulties supplying enough high speed processors, I wouldn't expect too much more clock speed headroom from most CPUs (particularly the mid-range models 733 and 800 MHz).
The Pentium III 933 will be released soon. Hopefully Intel will be able to supply their processors in quantities this time.
Of course we haven't forgot Intel's Celeron processor, which gives you an even better bang for the buck if you want to overclock it. We are already working on a similar article for Celeron and will post it shortly.