The National Maritime Museum, Greenwich has some excellent online collections related to maritime history and technology, including telescopes, marine chronometers, sundials, and a whole lot more. Some stuff I've been looking at: John Harrison's chronometers (described in Dava Sobel's book Longitude), polyhedral sundials, and pocket globes.
Astrolabes revisited: previously discussed here. Are astrolabes a way to navigate life? Want a free personal birth chart? How about an astrological weather forecast?
The Astrolabe: an instrument with a past and a future. You can even download your own Electric Astrolabe. (via finches' wings)