The University of Virginia's Electronic Text Center provides access to some full text documents and allows searching of a variety of texts.

British Poetry 1780-1910: A Hypertext Archive of Scholarly Editions at UVa

John Keats, The Poetical Works. 1884. from Columbia

Some other searchable full text databases include

A spectre I almost hesitate to raise: Project Gutenberg has as its goal the electronic distribution of VAST numbers of (public domain) texts. There's a lot here, BUT be warned that retrieving the full text of, say, Dickens' _Tale of Two Cities_ will take a while (it's about 800 K), so it's best to do this sort of work when demand is low --early mornings, weekends, etc. Once you've retrieved a text you CAN search it for a string (like 'heart') using the UNIX / command. With all that warning, here's how to get to an index of Project Gutenberg texts!