AMD Processors: Sempron 3300+, 3100+, 3000+, 2800+, 2600+, 2500+, 2400+
Intel Processors: Celeron D 351, 346, 345J, 341, 336, 331, 326, 320, 315
Intel and AMD both have their own low-end or "value" classification of CPUs. These low-end CPUs are more like scooters than automobiles. They'll get you where you need to go, but they won't carry a heavy computing load or move very quickly. Drop a PC with one of these CPUs in it onto a professional's desk and you'll probably make someone mad.
That said, however, these processors can perform basic computing tasks such as Web browsing, e-mail, and other non-CPU-intensive applications with a minimal consumption of power, so you'll have lower energy bills. In addition to slower processor speeds, these CPUs tend to feature small L2 caches, which constrain performance. On the bright side, less L2 cache results in much lower prices. We're talking $100 or less for this class.
Note: Intel's and AMD's CPUs run at different clock speeds. This does not indicate faster or slower performance.
Intel Celeron D processors: Intel has named its low-end category Celeron D. The "D" does not refer to dual-core. The model numbers range from the Celeron D 351 ($240), which has a decent 3.2GHz clock speed but only 256KB of L2 cache, to the Celeron D 315 ($70), which runs at 2.26GHz and also has 256KB of L2 cache. Beyond the clock speed, the key constraint in the Celeron D line is the front side bus speed of only 533MHz, which seriously slows down data transfer rates.