What's the best software for blocking pop-up ads? How effective is it,
how much does it cost, and can it be downloaded (as opposed to
ordering it online or buying it from a store)?

Since my experience with this kind of software is limited, I can't
give you a good comparison to help determine the "best," but I would
like to put in a good word for one pop-up blocker. It's called "Pop-Up
Stopper Professional," sold by a company called "Panicware." You can
download it here:

http://www.panicware.com/popupstopper.html

There's a free version of Pop-Up Stopper available for download here:

http://www.panicware.com/product_psfree.html

A chart that shows the features of the different versions:

http://www.panicware.com/popupstoppercompare.html

Here's an Epinions review of Popup Stopper Companion (an enhanced
version that sells for $39.95):

http://www.epinions.com/content_75855203972

The program Pinkfreud mentions works very well. However, I use a
browser that has built in pop up stopping that also works extremely
well and is free.

Its called MyIE2 and has a little bit of a learning curve, but is the
best browser I have ever used.

You can get it at http://www.myie2.com/

Regards,

-=clouseau=-

I also use MyIE2, and am extremely pleased with the perfomance.  

tlspiegel

Also, almost every web browser these days except Internet Explorer has
pop-up blocking built in. I'd recommend

Firebird: http://texturizer.net/firebird/download.html
Netscape: http://www.netscape.com/computing/download/
or Safari if you're on a Mac: http://www.apple.com/safari/

All of them are great browsers, in addition to having some nice
features not found in IE, such as pop-up blocking, tabbed browsing,
and built in Google searching.

I used POW by AnalogX for quite some time and I was fairly pleased. 
http://www.analogx.com/contents/download/network/pow.htm

I switched to Pop-up Stopper about a year ago though because it seemed
to function fast and smoother and also because it seemed to recognize
more of the little mosters than POW does.

regards;
tutuzdad-ga

I'd like to suggest Opera web browser. It's free as adware, and has
very good security, cookie and display customisations. www.opera.com

Owain

Here's a comparison of several products that might be of interest;

http://www.botspot.com/pages/comparison-pop-up-killers.html

I personally like "pop up killer", which has been a very good program
for me. Looking at their website, it appears that the program has been
discontinued, but if you can find a copy of it floating around
somewhere, it's one of the best available. Im not really sure if it
costs money or not. Here's their most recent website, which really
just has links to other popup killers and a "rip" kind of thing going
on: http://software.xfx.net/utilities/popupkiller/

Thanks to everyone for a hatch of great ideas. My most popular question ever!
McCook-ga