Computer parts dont sell the same way that toys and gadgets do... stores reduce prices on toys after Christmas because that's their big shopping season and they want to attract people back in to shop even more.
Computer parts drop in price when there is new technology being released ... the prices go down to move the old inventory. Around christmas time though I've seen prices jump a bit, not only to take advantage of the shopping blitz, but because some chip manufacturers shut down production in October for the rest of the year so supplies will drop by January. Low supplies mean higher prices.
If you're talking about computer cases, they can be bought just about any time of the year since the prices dont change often.
If you're talking about CPU prices you have to watch the product cycles.
Intel is set to release the P4 3GHZ chips in about 2 weeks, meaning the prices on current chips will dropa bit ... I'm waiting till then to buy one to save myself some money.