New package: pdfcomment
Though pdflatex provides the command pdfannot for pdf annotations it is somehow complicated to use. The new package pdfcomment offers a user-friendly way to insert comments/ annotations into pdf files.
pdfcomment requires the packages hyperref, xkeyval, ifpdf, marginnote and packages needed by them.
pdfcomment provides options for subject, author and color of annotations, supports icons used as graphics for pdf annotations.
For further information you could have a look at