More haftaros come from the Book of Isaiah than from any other Book of Prophets. Out of 54 parshiyos, 15 are from Isaiah (according to Ashkenazic tradition). Additionally, the haftaros for Yom Kippur morning, the last day of Pesach, a Rosh Chodesh that falls on Shabbos, and fast days at Mincha are all from Isaiah.
In the summer, we have a long series of haftaros that come from this Book. These are called the shiva d'nechamta, the seven of consolation. They begin with the Shabbos following Tisha B'Av, which is called Shabbos Nachamu. The Shabbos actually receives its name from the haftarah, which begins, "Nachamu, nachamu, ami," "Be comforted, be comforted, my people." This comes from Isaiah chapter 40, which is read as the haftarah for parshas Va'eschanan. The following weeks are from the subsequent chapters, although not in strict chronological order. They are:
* Eikev - from the middle of chapter 49 through the start of chapter 51
* Re'eh - middle of chapter 54 through the start of chapter 55
* Shoftim - middle of chapter 51 and most of chapter 52
* Ki Seitze- - the first part of chapter 54
* Ki Savo - chapter 60
* Nitzavim - the end of chapter 61 through the start of chapter 63
(It may be curious that haftaros frequently start and end mid-chapter. The chapter and verse system was invented by Christian scholars. It's a very useful tool, but it doesn't always jibe with our tradition as to where topics start and end. That's why aliyos and parshiyos frequently don't line up with the chapter breaks a verse or two off.)
Unlike most haftaros, the "seven of consolation" do not relate to the content of the weekly Torah reading. They are meant to comfort klal Yisroel after the sadness of Three Weeks commemorating the destruction of Jerusalem and the two Temples. They are all taken from Isaiah, as the last third of his book focuses heavily on the theme of consolation.