So OEM doesn't mean that it is a leftover crap
Not at all. With one or two exceptions, like the video card case I mentioned, the actual product you're buying will be exactly the same. Hardware manufacturers basically sell OEM products as a service to system builders, who don't need thousands of boxes to unwrap and throw away, and don't care about things like cables, when they already buy them in hundred thousand unit lots - and to savvy home computer enthusiasts who like to bargain-hunt. If you don't need the extras, then you're in the clear, and you can easily shave a couple hundred dollars off the cost of your new computer.
Just make sure you get a warranty, that's right. I'm checking out TCWO now, another very reputable hardware seller. Here's their warranty rule, for Athlon XP CPUs. If you buy an OEM CPU, you need to buy an AMD-approved cooler, from them, at the same time, and you get a one-year warranty. Otherwise, it's a 15-day warranty. AMD CPUs run VERY hot, and without proper cooling they literally burn up, due to no thermal protection - so you can understand the strict warranty rules. If you buy a retail CPU, you get a three year warranty. In the case of the 2100+, they sell the OEM flavor for $169, and the retail for $194. That leaves you $25 to buy your cooler with, if you want to break even (which is why I mentioned that unless you already have a cooler, or you are a very demanding customer with regards to CPU cooling and don't want to use the retail cooler, going OEM with CPUs doesn't necessarily save you money).
But speaking in terms of just the warranty, with regards to CPUs, three years versus one doesn't mean a hell of a lot. If a CPU lasts one year, it's most likely going to last ten or fifteen years, or "forever", as long as you're keeping it cool and not overclocking. I personally have never seen a CPU that didn't work, unless the owner was overclocking it and burned it out. In my basement, I've still got a Tandy 1000 and an Amiga 1000, both from 1985, that fire up whenever I want them to.