Avery Index - premier index for architecture journals, includes architectural history, urban planing, theory and preservation.
Other Art Journal Containing Architecture in order of usefulness/importance
Art & Architecture Source (formerly Art Source) - the major journal article source for art; 1929-present.
Kubikat - online article and book catalog of five major European art libraries. Multilingual
Artbibliographices Modern - just 19th-21st-century art topics; good on architects.
Humanties Journal Databases
JSTOR - limit to "architecture" or "history". Don't forget you can search by image contained in article by "caption" search.
Arts & Humanities Citation Index - (Web of Knowledge) - look up scholarship by whom was cited in the article. Great for reviews!