There are few surprises here: the most frequently-cited papers are those offering novel scientific methods or easy implementations of those methods. The Altschul BLAST papers are a great example. They describe sequence comparison methods which are so easy to use and powerful that everyone from undergraduates to senior researchers still find them useful on a daily basis. Of course, methods eventually become common knowledge and people either stop citing them, replace them with newer methods, or just forget who created the methods in the first place. Laemmli buffer, described in a 1970 paper by its namesake,** is still used in proteomics studies, but so is LB medium, a recipe originally described as "lyosgeny broth" but often called "Luria-Bertani" medium after its creator, Giuseppe Bertani, and the microbiologist Salvador Luria.***
*Apologizes if you can't access content behind the paywall! I'm not sure if this article is broadly accessible but it really ought to be.
** Yes, that's right, the seminal paper by Dr. Buffer.
***The 1951 paper is here. This 2004 review offers a nice historical perspective.