check the rating in this link here... blue column on the right side... http://www.carsound.com/review_archive/amps/jl_5001.html

I just got the jl 500/1 amp from a friend with external gain knob and cant wait to put it in and I too have been hearing good reviews about this amp

the bass control knob is the only thing I need for mine :) but I don't feel like spending $50 on it for some reason, don't really think it's worth it. But yes the amp is great. Doesn't have a built in fuse also, like the old fosgates that didn't have their power ratings set in stone kinda thing.

I would have to say: For 95% of the population that will be connecting their high power amp with a less than perfect installation, the JL makes perfect sense. Good power with crappy current supply to an amp will surely produce less than adequate results considering the added cost of capacitors, upgraded wiring, or the effects of improper impedance matching.
A well regulated supply is called for in thse situations.
For the few lucky enough to have the benefit of an incredible installation, then an unregulated amp will get you more watts/$ as far as the amp goes. Perhaps the overall cost depends more upon your installer than upon the particular brand of parts that he uses.

The real trick is to find the combination that works best for you.

The JL will give you enough power to pound., won't be capable of the total thermal limit of your sub without distortion, and when you do overdrive it, you'll have a bit of time before you do serious damage to your sub. All in all a good mix of trade-offs.

If you want better, and are sure you are up to the task (currently speaking), then there might be better choices available. But only if you "do it right."

Thanks for the reply. Just to clarify, the only reason I was going with the JL Audio 500/1 is because of their reputation, quality, and the amazing deal that I got for it. I know I might be underpowering my subwoofer, but people are telling me that they are moderately rated, so the actual RMS rating is higher than just 500 watts. I don't know whether this is true or not, because some people are saying that I can get more while others are saying that 500 is the maximum I can expect to get from my JL Audio amplifier.

Jl amps do what they say and more as far as rms goes. Now dont go thinking you will get 600 or 700rms out of it cause it wont happen. The 500/1 will most likely do more than 500rms, but how much more i cant tell you. get the amp properly bench tested and find out. other than that it is a great amp, and you will be happy. remember its not all in how many watts you run that decides how loud your system will be. most of it is in the install.

CarSound tested the 500/1 back in 2002:

Output Power (Resistive) (4 ohms @ 60 Hz to 1% THD+N): 605 watts @ 14 volts; 601 watts @ 12.8 volts; 591 watts @ 10.5 volts
Output Power (Resistive) (2 ohms @ 60 Hz to 1% THD+N): 620 watts @ 14 volts; 604 watts @ 12.8 volts; 598 watts @ 10.5 volts
Output Power (Reactive) (4-ohm IHF Load @ 60 Hz to 1% THD+N): 639 watts
Output Power (Reactive) (2-ohm IHF Load @ 60 Hz to 1% THD+N): 733 watts

http://www.carsound.com/review_archive/amps/jl_5001.html

It didn't become the best selling amplifier in the USA by delivering less than it promises.