I've got a Yamaha EMX512sc powered mixer, that is great for simple PA setup. It's got 2x500 watt amps in it. You could use one for your mains, and the other for your monitors, or you one for left, and the other for right.

>Yamaha EMX 512sc<

I used to use a single JBL JRX125 speaker cabinet (2x15's and a horn), and two floor monitors, and never had any trouble hearing the vocals.

If your PA is only going to be used for vocals, I would suggest getting 2 1x12 PA speakers. The Yorkville E12 is probably one of the best for this application. A pair of those and a mixer like that yamaha, and you're in business. Expect to spend atleast $1000 for a decent PA that will actually let you hear yourself.

If that's a little out of your price range, just look for the speakers with the highest sensitivity rating you can afford.

I'll throw out a few suggestions here... >Yamaha Club Series 1x12 cabinets< >Yamaha A12< >Peavey PR12< >Yamaha EMX312sc< >Peavey XR600G< >Peavey XR 8300<

And then, don't forget about your mic's, mic cable's, mic stands, speaker cable's, and speaker stands.

Don't let anyone fool you into thinking that bigger is better. 15" speakers are ok if you're gonna be micing instruments, but with vocals, they can get a little bassy and make the vocals get lost in the mix. 12" speakers tend to let the vocals cut through he mix better. Also, if you intend on running bass and/or kick drum through the PA, you'll definitely want to think about getting a pair of subs too. If you do that, you'll need to look into getting a separate power amp to push the subs, and bass and kick drum need a lot of power, and also a crossover to keep the right frequencies going to the right speakers.