At the most recent New York R User Group meetup, the topic was creating graphics in R with the ggplot2 package. Drew Conway's talk, "Making pretty pictures with ggplot2" gave several practical examples of visualizing data with ggplot2 and is well worth checking out:
You can follow along with Drew's slides, which are downloadable from his blog. (Update: you can now also watch the video and slides in sync -- thanks, Drew!.) You'll also find there video and slides of another talk, "Introduction to the Grammar of Graphics with ggplot2 in R" from Harlan Harris.
Zero Intelligence Agents: Visualizing Data with R and ggplot2 (Video)