Popping up with what I'm guessing will be the outside-the-norm answer, right at the start:
A link to the subscribe page.
Why -- because I'm not in the business of irritating people with pop-ups and squeeze pages.
My viewers are repeat shoppers (this is referring to a gift shop website) so the key is keeping them HAPPY with their surfing experience. The happier they are, the more they spend, and the more likely they will come back to spend some more in the future.
Also, squeeze pages are not valid opt-ins for mailing lists, unless we fully divulge to the visitor that they are signing up for a list & what they should expect from that subscription. Understand this isn't a judgment call... this is from the upstream/backbone/data center level. I deeply value my servers, so I don't tempt the wrath of my data center nor my upstream providers.
And, many internet shoppers are reluctant to divulge personal data about themselves before at even browsing the product selections. I know I am no exception to this; when I was camera shopping last November, for example, I visited easily 20 different websites. Only 2 were given my personal information though.

Sites which tried to force information out of me prematurely, while I was still in the "shopping around" stage, were quickly crossed off my list. I left and never came back.
So that leaves pop-ups, or links? People are much less irritated by links. So, links it is.
...just explaining the reasoning in-depth, because I know the high marks that pop-ups get simply because of the high subscription rates -- which is totally cool.

In many instances I think pop-ups are great, but I also think there are some instances where they are probably not the "best" method.

Bailey