Does anybody have a good example for Time Series Forecasting/smoothing using Kalman Filter in R?
In addition to the packages mentioned in other answers, you may want to look at package forecast which deals with a particular class of models cast in state-space form and package MARSS with examples and applications in biology (see in particular the well-writen manual, Chap. 5).
For general applications, I aggree, though, with the previous answers, with dlm being in my view a versatile and powerful package (well described in the book Dynamic Linear Models in R, by Petris et al.), KFAS offering routines which implement most of the algorithms described in the excellent Time Series Analysis by State Space Methods and FKF with limited facilities and no examples, but being the fastest.
For good examples look at the dlm vignette I would avoid all the other packages if you don't have a clear idea of what you want to do and how.
The package stsm is now available on CRAN. The package offers some utilities to fit the basic structural time series model.
The packages mentioned in other answers provide flexible interfaces to cast a broad range of time series models in state-space form and give sound implementations of the Kalman filter. However, in my view, little attention is given to the procedure that optimizes the likelihood function. A general purpose algorithm --the L-BFGS-B algorithm-- is typically used. The
stsm package enhances the standard procedure and provides specific algorithms to fit the basic structural model.
Further details are given in the the document provided with the package. For a quick example you can also see this post.