1898 Annexation - a bibliography on the subject.
The Annexation Of Hawaii: A Collection Of Documents - the beginnings of an online collection of relevant documents from the University of Hawaii at Manoa.
An Annexation Time-Line - through December of 1898, up to the Treaty of Paris.
HAWAIIAN ANNEXATION RESISTANCE - 1897 - from right before annexation, a history of resistance to the proposal.
Modern History Sourcebook: Annexation Of The Hawaiian Islands, 1898 - the actual text of the joint resolution to annex the islands.
NoodleLinks: Hawaiian Annexation - somewhat disorganized source list, a good chunk of it being online.
Territorial Years - The History of Hawaii - Hawaii School Reports - brief, but really interesting, covering the years 1898 through 1959.
Two Views of Hawaiian Annexation - from a larger essay on Mark Twain and Hawaii, giving Twain's changing views on the subject.