Play chess online and get an offical Elo rank I played chess 30 years ago an now I am back in the arena. I have some spare time to train and play online. Could you please recommend me a good place to do so. A web interface without the need of any special clients would be great. Even greater would be the possibility to earn an official FIDE Elo ranking to see my progress.
There is one (and so far only one) place where you can get the official FIDE rating - the FIDE Online Arena. It however needs a client. A quick introduction is here and the arena is at http://arena.fide.com 

I have not tried it so I cannot comment on how good the interface is but I assume it is good. The killer feature is that it calculates official FIDE rating, which is calculated the same way as the official rating for over the board play thus they are directly comparable. Even better they are linked - every time a new FIDE rating list for over the board play is published this rating is incorporated in the online rating (in other words games played over the boards count to the online rating too). It does not work the other way around. 

A very little known fact so far is that FIDE has introduced new players titles, so called FIDE Titles for the Lower Rating Band. Official info here and some basic info here. You earn these titles for online play but the cool thing is that they are valid for life and you can use them in over the board play as well. As an example if you consistently keep your online rating above 2000 you will become an Arena Grand Master (AGM). 

It is very likely, and I would bet on it, that in future all most popular online servers will offer calculating the official rating too. This may take some time though.