David Smith notes that CRAN is now up to 10,000 packages:
Having so many packages available can be a double-edged sword though: it can take some searching to find the package you need. Luckily, there are some resources available to help you:
MRAN (the Microsoft R Application Network) provides a search tool for R packages on CRAN.
To find the most popular packages, Rdocumentation.org provides a leaderboard of packages by number of downloads. It also provides lists of newly-released and recently-updated packages.
R is a big language; having good heuristics for figuring out where to find appropriate packages is extremely important.