I thought I would add a few thoughts to MightySaturn5's suggestions about purchasing or matching up power amps with speakers. His remarks were excellent, by the way.

How many watts should your speaker handle vs. the size of your amplifier? To answer that, let's talk first about how a speaker can fail. There are two basic ways:  thermal failure and mechanical failure. 

Thermal failure is when a speaker is stressed to the point from too many watts (of  "clean" sound -- more on that later) for too long a time that it frankly just overheats and dies...components melt, things fry, and it quits. Kind of like a seized engine in the automotive world.

Mechanical failure usually occurs when a speaker is driven by an amplifer that has exceeded it's maximum output. For example, if you have a 50-watt amp, and turn it up, it will put out 50 watts (theoretically) of clean sound. However, it will also exceed 50 watts if you keep turning it up, but the sound will be distortion (square waves on an ocilloscope). This distortion will kill speakers quickly at excessive volume; it causes over-excursion of the cone and speaker parts which begin to disintegrate, leading to speaker failure -- from component failure, not from heat. So it is easily possible to blow out a 400-watt speaker with a 50-watt amp if you drive it into clipping (=distortion).

So the key is to match your amp output with your speaker's ratings. If you have a 250-watt RMS speaker load (follow MightySaturn5's advice about ohm loads and amp matching), match that with an amp that puts out at least 250 watts. You can use an amp with less power, but be care not to overdrive it. If possible, use an amp with a higher output rating than your speaker load (like a 300-watt amp into that 250-watt speaker load). That way, you'll hit your speaker's maximum before your amp ever clips. (Of course, exceeding your speaker's maximum rating with clean sound will produce distortion, too -- but from the speaker, not the amp.) The speaker might eventually fail from too much heat, but you'll do it with clean sound, not amp distortion which will happen a lot sooner. The bottom line is always buy the biggest amp you can afford if you plan to really turn it up!