Often called x86 or (less commonly) 80x86 because the original version was named 8086, and subsequent revisions were numbered 80286, 80386, 80486, etc. After that, Intel changed the naming scheme, since numbers can't be trademarked. So the 586 became the Pentium, and the 686 (logically) was called the Pentium2, which is what happens when marketing has too much control of a company.
Chips like the Celeron are like the Pentium2, but often have something disabled (in this case, they have a lot less on-die Cache).
The are two main manufacturers of these chips:
AMD's offerings include the lower cost Duron (similar to the Celeron in that it has a small cache), the Athlon, and now the 64bit Opteron.
Which is better is a traditional ReligiousWar/FlameWar - many people believe that AMD offers better value (performance/price) while others believe that Intel chips are more reliable.
