The current numbering scheme from Intel is quite a disaster and the Inquirer heard Intel will soon introduce a new processor numbering scheme. However, this isn't something to be happy about is things will get even more complicated than before.
The newer system uses letters and numbers in the form X00, the first letter being the the class differentiator, the first number most likely being the family, the second being speed, and the two trailing zeros add '1337'-ness.
Yonah could well be the first to get the treatment, and it appears as if it will be dubbed the x1x00 series. The normal processors will be labelled T1x00, low voltage will be L1x00 and ULV models will be U1x00. Got that? But the situation will become more confused when the Merom family of cores is launched. Merom itself is another T', but the second number is either a 4 or 6, and I have no idea what the difference is, speed is the next number. Possibly cores, but who knows.
For the desktop, Conroe will get the dreaded S moniker, and it seems all the Conroe variants will stick with the same letter. Higher variants will get higher numbers, capping out at 5 for Conroe. One source said Allendale will be a 2, another denied that. Either way, look for S5x00 for this line with others to follow.
More details about Intel's upcoming numbering scheme can be found over here.