Dr. Hans Reich at the University of Wisconsin has a hobby. He maintains one of the most extensive chemical databases on the internet, free of charge. The information spans from raw values like pKa and NMR shifts to comprehensive lists of named reactions (links to Smith and Chempen), reagents and rules.
While it’s easy to lose a few hours just browsing, I’d like to highlight the 1H and 13C shift data as especially useful. Chemical shifts are broken down by functional group, then subdivided by neighbouring functional groups. The end result is similar to one of the shift charts from undergraduate courses, on steroids, providing specific values to common structural motifs (and some less common ones as well; I challenge you to draw an azoxy diazene oxide). While not a complete replacement of Chemdraw’s prediction tools or a database like SDBS, these tables have come in handy more than once.