Lots of shows are available online now, so if there's anything you've been wanting to catch up on, this is your chance.
At ABC watch streaming feeds of all of this season's episodes of Grey's Anatomy (which you've missed because you're watching Supernatural, right?), Desperate Housewives, Lost, Brothers and Sisters, Ugly Betty, and What About Brian.
At NBC, catch all the available episodes of Friday Night Lights, Heroes, and Identity.
CBS has CSI, CSI: Miami, CSI: NY, How I Met Your Mother, Jericho, NCIS, Numb3rs and Survivor.
Fox makes things harder to find, but on their MySpace page you can see episodes of Prison Break, Bones, The Loop, American Dad, Standoff, Vanished, Talk Show and 'Til Death.
The CW is supposed to be beta testing streaming video of some of their shows, including Supernatural and Veronica Mars, but in the meantime these shows are available at iTunes (and no, you don't have to have an iPod or a Mac to watch these--in fact I find them easier to watch on my laptop because the screen is bigger), along with lots of others. It appears they've upgraded the quality of the files, too, making them even more worth the $1.99 per episode.
So, if there's a show you've been curious about, or have just missed catching up on, take advantage of these new outlets to sample or get back up to speed.