Index Medicus was probably the first really high-end reference source I can remember using in college -- for a paper on methemoglobinemia. I remember being so astonished that you could attain that level of access to medical information, and that it was available even to scrubs like me. This was back when online searching was pay-by-the-query Dialog searching and available only to highly skilled library staff. Now it's 16 years later and the print version of Index Medicus is ceasing publication due to lack of subscribers, only 155 subscribers last year.