new alternator?

[greasemonkey]

I'm pretty sure my alternator's going out. All my lights dim and flicker at lower RPMs, and just recently there is this really annoying high-pitched squeal coming from it.
I really don't care if it is a one-wire setup, I just need a new one. From doing a search, I have found that everyone thinks that internally regulated ones are the best.
What's a good replacement, maybe higher output alternator to get? Should I just go to the parts store and ask the dude behind the counter (that's what worries me, some of those guys will sell you anything, even if it isn't for your car ).
Thanks everyone.
John