Having recently upgraded emacs to the latest version (I was running the last release of CarbonEmacs), I took the opportunity to clean up my .emacs file and add/enable a few new packages:

• smex: provides ido-like completion of M-x commands
  
• ropemacs: this looks really useful for python programming. Docstring lookup, name completion, refactoring.
  
• darcsum: interactive darcs recording
  

Packages I've been using for some time:

• ESS: Run R in an emacs buffer. Easily run bits of code in the running R process.
  
• AucTeX: edit and compile LaTeX documents
  
• doxymacs: package to easily insert doxygen comments
  

Deprecated packages:

swbuff: cycles between buffers with a single keystroke, similar to how you can move between tabs in a browser with C-pagedown and C-pageup. I now use ido for this, using the following lines in my .emacs file:

(add-hook 'ido-setup-hook 'ido-my-keys)

(defun ido-my-keys ()

  (define-key ido-completion-map [C-next] 'ido-next-match)

  (define-key ido-completion-map [C-prior] 'ido-next-match)

)

(global-set-key [C-next] 'ido-switch-buffer)

(global-set-key [C-prior] 'ido-switch-buffer)