What watts what?

1000 watts will usually fill anything up to a good size bar.  Above that and you need a real professional rig with multiple speakers, subwoofers, etc.

In general, speakers can be connected to amps that are as much as twice as big: 500W speakers to 1000W amps.  It's clipping that kills speakers, not raw power.

Can you describe your current system in more detail?

-Laz

Think of Ohms like the engine of your car. The wider you open the throttle the more power the engine puts out - look at the spec and you will see something like "250Bhp @ 3500 Revs", that means max power is at 3500 revs. Both higher and lower revs produce increasingly less power. Ohms works in a similar fashion - the less Ohms you have, the less resistance you have (like opening the throttle lets more air through) and the more power comes from the amp.
A 1500W power amp will be marginally louder than a 1MW amp - to double the volume on your 1MW gear you would need to uprate it to 10MW (10,000W).
I think I'd be looking at the speaker arrangement and whether adding more speakers wouldn't give more output. than a new power amp.

Currently we have two 15" main speakers.  We have 4 monitors.  We have one Carvin 950watt power amp and a 16 channel mixer.  We have a subwoofer but we don't use it.

We could get another sub and two more power amps.  But I think I'd like to get two new main speakers with dual 15s in them and a new huge power amp.  Then we could use the old amp for the monitors.

I want to get two of the big ones, what do you think about this series?

http://www.jblpro.com/soundfactor/sf_home.html

Since my last post I got a Carvin DCM 1500 watt power amp and the JBL dual 15" towers.  They truly pump the sound.  There is no need for subs.  Our system rocks!  I highly recommend them.

Nice PA.

I looked up some specs. That Carvin DCM amp puts out 2 X 300W @ 8 Ohms, 2 X 500W @ 4 Ohms, and 2 X 750W @ 2 Ohms.

Those JBL's you showed are the SF25's. They are 4 Ohms. Rated 500W continuous, 2000W peak.

So if you run one SF25 off of each side of your amp they will get 500 Watts each. You could use your 950W amp to power your 4 monitors.

That's a nice setup.

Invest in a dual 31-band EQ. One for your mains, and one for your monitors.

An EQ is primarily used to control feedback and to adapt your sound to different venues.

What are you going to be running through your PA?

We usually run two vocal mics.  The drummer likes to mic his bass drum.  The guitar players use a Marshall Mode 4 and a Peavey 5150 half stacks which have line outs.  I believe we will run the stacks into the mix as well.  

Guitar speakers are designed for distortion, PA speakers are designed to give the cleanest reproduction of sound (the human voice). The "experts" will usually recommend you mic your guitar amps. Shure SM57's are a popular instrument mic. This way the PA will reproduce the distortion of your guitar speakers.

Bass is usually played very clean, so it usually sounds great straight into the board.

If you are new to PA's try this site.

http://members.cox.net/pasystem1/

I have been going on there a few years. Real nice people who know sound. Read the tutorial, that will tell you a lot about proper setup and operation of a PA.