Berlin Marriott - big institutional hotel, but superb, convenient location in one of the great modern cities of Europe.
Boston Custom House - the Eagle Suite is one of the most memorable hotel rooms ever. Killer views of Boston Harbor; nice living/dining area; being on the balcony between the Eagles makes you part of a Boston landmark.
Budapest Marriott - stunning Danube river views, but my all time favorite concierge lounge - outrageous roof deck, plentiful/tasty/diverse food, great location.
Guam Marriott - sure, the place is a tad dated and it could use a renovation, but the corner balcony, overlooking Tumon Bay - uninterrupted view in both directions - takes the cake. Wonderful staff, tasty fruit waters (changed daily), and good snorkeling right outside.
Marriott Plaza in Buenos Aires - location,location, location...
Niagra Falls - the Fallsview Family Suite is just plain stunning. I'm no fan of the region, but the Falls are awesome (and the Maid of the Mist rocks), but the VIEW from that suite! We sat in the window for HOURS (day and night)!!!
[I'm deleting the Renaissance Chancery Court, London. I recently learned that the Chancery Court is no longer a Renaissance property. What a shame!) - what an amazing building (and sublime service); larger-than-Euro-style rooms. As a fallback, I do like London's Grosvenor Square (for location).
Renaissance Harbour View Hotel Hong Kong - killer views. The Renaissance on the Kowloon side is also quite good, but the location is better on the Hong Kong side.