The jqModal is an "oldie but goodie" plugin. It's been around for a while and revved a few times and has been pretty reliable for what we've used it for.

http://dev.iceburg.net/jquery/jqModal/

I've gotta admit, initially getting it working was a bit frustrating for me at first. At the time (a while back) I had just started exploring jQuery modal plugins and wasn't really sure which would do the job. I sunk some time into this and after some initial stumbling, gave up. Then I messed with some others and was like, "fark, that sucked" (especially with cross-browser checks), and came back to this one.

Glad I did. Once I figured out how to get it set up (the css matters a lot, take a good look at the examples), it did the job and I've used it in a bunch of projects since then, which also gave me some opportunities to try more of it's features. All panned out well.

This is a nice one to use when something like jQuery Thickbox feels like overkill and you're really looking mainly to show dialogs and messages. We've had some other cases where we needed to show external sites in the modal and for those cases opted for Thickbox or the jQuery UI dialog widget, though there's a 3rd party example of opening an external site at the bottom of the jqModal examples (I haven't tried it).