Clustering

• Clustering in R: R examples on various clustering techniques, with R codes and dataset provided. See section 4.15 in the link for exercises instructions.
  

Text Mining

• Text mining with Twitter and R
• Getting Started with Latent Dirichlet Allocation using RTextTools + topicmodels
• Word clouds for document comparison
  

Time Series Analysis

• An R Time Series Tutorial

Social Network Analysis

• Tutorial on Network Analysis with Package igraph
  
• R for Social Network Analysis
• Community Detection In R

Sentiment Analysis

• Tracking US Sentiments Over Time In Wikileaks

Visualization of Spatial Data on Maps

• A Napa Valley wine tasting map, made with R and ggmap
  

R Programming

• R Tips: lots of tips for R programming

Graphics

• Learn R Toolkit
  
• Using R for advanced Charts
• Slides on R Graphics by Paul Murrell:
  It provides examples on advanced graphic controls.
  
• 3D bar charts, matrix contours, microarray heatmaps, network graphs, scatter & pairs plots , Ramachandran (phi/psi) plots, and linear models
• Interactive charts with googleVis package and R
• Easy maps with R and googleVis
• R graphics gallery with source code

Parallel Computing

• Examples of parallel computing in R with the multicore package

Big Data

• Handling large data with package ff and ffbase

Debugging and Error Handling

Database Access and Others