Daily(ish) Database: scriptures.byu.edu
What it is: scriptures.byu.edu is an interactive compilation of all the scriptures that have been cited in General Conference talks from 1942 through the present day.
How to use it: I prefer to do scripture study by topic or theme rather than chronologically, so this database provides a nice way of navigating between more loosely related topics that won't necessarily be cross referenced in the Topical Guide. I can start with a scripture I really like, find General Conference talks which touch on the same topic, and find the other scriptures cited in that talk. Or I can start with a talk I really like and have easy access to the original context of all the scriptures cited.
Another cool feature is the ability to limit your search by speaker, so you can see only the talks and scriptures cited by your favorite (or least favorite) GA.
Lastly, it's just kind of fun to look at the statistical distribution of the cited scriptures as a measure of which topics and doctrines are considered most important. (E.g., Matthew is the most commonly cited gospel, Ether 12:6 has been cited 29 times since 1942, and the Song of Solomon hasn't been quoted in General Conference since 1979.)
Pros and cons: I'd like to be able to see a few more types of limits available, such as limiting by a year or a range of years. Also, I don't see myself ever making much use of the full text of the earlier General Conference talks. (It seems like they tend to be pulled out only for arguments on points of justifiably obscure doctrine.) These are, however, fairly minor quibbles when it comes to such a slick database.