What is the modern lightbox / modal option now and going forward?

Answer 1

I use http://www.slidesjs.com/ (jquery plugin) for slides and Twitter Bootstrap for modals.

Answer 2

There are a few things to consider when selecting a modal option:

1) Is it responsive? Responsive design is the future, whether you like it or not.
2) Is it usable? Most modals exist over a black overlay that prevents the user from accidentally interacting with the content underneath, but if that black overlay is clicked/tapped the modal should go away.
3) Does it have an animation? Some use jQuery to animate (bad), some use CSS3 transitions (good).

For more information on #3, check out: http://paulirish.com/2012/why-moving-elements-with-translate-is-better-than-posabs-topleft/

I use Bootstrap modals. They are easy to implement, restyle, and make responsive. After watching Paul Irish's video from the link above, you'll also understand why I appreciate that they achieve animation with CSS3's translate3d().

Answer 3

A few options to consider:
http://www.benplum.com/formstone/boxer/
http://i-like-robots.github.com/jQuery-Modal/
http://docs.toddish.co.uk/popup/demos/

all still relatively young but in most cases enough to suit your needs.

A big +1 for http://www.slidesjs.com/ if you don't need a modal window.