Bookends is on sale for 50% off today April 3, 2008 only over at the MacUpdate Promo. Although I haven’t tried Sente in a while, when I was doing my senior thesis Bookends was the best reference software on the market for Macs (Sente had a nicer interface, but didn’t support the social sciences as well; probably more appealing if I were in medicine). If you do research, you really ought to give Bookends a look; it’s an invaluable tool, even if it’s a pretty ugly program at first glance (although maybe version 10 has a more Mac-like interface; I primarily used version 9).

MacUpdate usually runs some level of sale on the software for a few days or weeks after the initial promo, too, so even if you miss the one-day 50% off deal it would probably be worth checking out.