Just as the Pentium III was a Pentium II with SSE and a few added features, the Celeron II is simply a Celeron with a SSE, SSE2, and a few added features. The chip is available from 533 MHz to 1.1 GHz. This chip was basically an enhancement of the original Celeron, and it was released in response to AMD's coming competition in the low-cost market with the Duron. The PSN of the Pentium III had been disabled in the Celeron II, with Intel stating that the feature was not necessary in the entry-level consumer market. Due to some inefficiencies in the L2 cache and still using the 66MHz bus (unless you overclock), this chip would not hold up too well against the Duron despite being based on the trusted Coppermine core. Celeron II would not be released with true 100 MHz bus support until the 800MHz edition, which was put out at the beginning of 2001.
Duron (2000 - Current)
In April of 2000, AMD released the Duron "Spitfire". Spitfire came primarily out of the Athlon Thunderbird lineage, but it had a lighter load of cache onboard, ensuring that it was not a contender in the performance realm with its big cousin. The chip had a 128 KB L1 cache, but only 64 KB of on-die L2. Despite the lower L2 cache, internal methods of dealing with the L2 cache coupled with other improvements make the Duron a clear winner when compared against the Celeron. Duron also works with the EV6 bus while Celeron was still working with 66 MHz bus, and this did not help Celeron at all.
In August of 2001, AMD released the Duron "Morgan". This chip broke out at 950 MHz but quickly moved past 1 GHz. The Morgan processor core was the key to the improvement of Duron here, and it is comparable to the effect of the Palomino core on the Athlon. In fact, feature-wise, the Morgan core is basically the same as the Palomino core, but with 64 KB of L2 rather than 256 KB.