The Responsa Project,
which includes the Talmudic Enclyclopedia. It's a present for our 25th Wedding Anniversary, which isn't for another two months almost, but, hey..
If you have an older version, they'll send you a brand new upgraded disk at a discounted price - a heavily discounted price.
I C+Ped the list of books that the newest version contains - and the list was 21 pages long on Word. If one were to purchase those books, they'd be many tens of thousands of dollars.See here:
Plus the disk has the following features: