The WGA strike is three days in, and it's already taking its toll on Hollywood. The verdict? More reality, less scripted television, including early appearances of shows that don't usually come until the summer. You can look forward to the early appearance of Big Brother, for example, on CBS, since it eats up three hours of prime-time programming, and is immune to the strike. The show usually airs in the summer, but it's crisis time for the networks, so it's looking like it will arrive early.
In addition to late-night shows such as The Tonight Show and The Late Show With David Letterman, other "strip" shows are looking at reruns in the not-too-distant future, such as Jimmy Kimmel Live and even the network soaps, which should run out of material right at the end of the year.
Many shows are completed for the season, but many are midway done or not even close. On the full side, there are shows like The Tudors, Cane, and Jericho have all reached their season commitments, while shows such as Entourage and The Wire are not even started for next season, and will not start until the strike has concluded, which means that it might be a long, long time before we see those shows back on the air.
Sadly, the strike might curtail the final seasons of shows like Scrubs and The Shield, which might never go back into production, and would end with a whimper, should the strike continue as long as it looks like it will.
The Los Angeles Times has a pretty handy grid of where all the shows you might care about fall in terms of how much production they have completed for the rest of the year. It should keep you up to date.