The 44 volume İslâm Ansiklopedisi is reason enough to learn Turkish. And its companion website is, as far as I can see, absolutely brilliant.
The website has a very clean interface with clear options for searching. It even includes little buttons for letters specific to the Turkish alphabet. Upon a search, you will see a list of entries corresponding to your search, and you can click to see the entry. This is actually shown in a different frame, so you can already engage in a new search while still reading an entry.
These entries are presented in plain text – what a godsend. This allows for easy copy and pasting (for example into Google translate). The editors of the website totally get it because they also include a button to see a PDF of the original pages of the encyclopedia. This way you can be assured that the text and page number is genuine.
Access is free – let us hope it stays that way.
The Digital Orientalist 
For those of us without Turkish, can you explain furthermore what this site entails? Thanks.