Hi Aycan, No difference between two. 책 이에요. 책 입니다. This one sounds formal

In Korean there is polite and formal way to say. 책입니다. ㅡ It is 하십시오체 (very polite and formal way of speaking) 책이에요. ㅡ It is 해요체 (polite and informal way of speaking) cf) 체 = style / 하십시오체 = 하십시오 style formal polite ←-----------------------------------→ impolite 하십시오체 - 하오체 - 하게체 - 해라체 informal polite ←→ impolite 해요체- 해체

The difference is in speech level. There are seven speech levels in Korean, and each level has its own unique set of verb endings which are used to indicate the level of formality of a situation "입니다" is Hapsyo-che(합쇼체) It is used between strangers at the start of a conversation among male co-workers by TV announcers to customers "이에요/예요" is Haeyo-che(해요체) It is used mainly in Korean phrasebooks for foreigners between strangers, especially those older or of equal age between female co-workers or friends by younger speakers as a less old-fashioned alternative to the hao-che. by men and women in Seoul as a less formal alternative to the hapsyo-che. Refer to http://en.wikipedia.org/wiki/Korean_speech_levels

This is a book. Book.