UKRlib.com has one of the largest online collections of Ukrainian literature. The full text of hundreds of works are available here along with biographical information on many authors, a dictionary of literary terms, the texts of many folktalkes. Truly a rich source for anyone seeking Ukrainian literature in electronic form. Most of the documents can be downloaded as zip files or read online.
Ex Libris Ukrainian Electronic Library provides digital access to an extensive list of Ukrainian literature.
Biblos.org provides forums and access points for all kinds of literature. The compilers especially encourage additions of "Samizdat" literature at this site.
If you are interested in contemporary Ukrainian literature it is often helpful to see what is making their "Bestsellers" list. Both Avtura.com.ua and Ovista.org.ua have lists of the most popular books. Avtura.com.ua also has a very handy list of online bookstores for Ukrainian popular literature. Click on the link for "Книгарні" at this site for a list of links to Ukrainian bookstores online. There is a list by region and a list by store name.