My memory is marked by the titles of two papers by Branko Grünbaum:

 1. Branko Grünbaum. `[Are your polyhedra the same as my polyhedra?][2]' *Discrete and comput. Geom.: the Goodman-Pollack Festschrift*, ed. B. Aronov et al, Springer (2003), pp. 461-488.

 2. Branko Grünbaum. `[The Bilinski Dodecahedron and Assorted Parallelohedra, Zonohedra, Monohedra, Isozonohedra, and Otherhedra][1]'. *The Mathematical Intelligencer* (2010). DOI: 10.1007/s00283-010-9138-7.

The first title is easy for me to recall whenever I need to refer to the paper. The second title sounds fancy (though the article itself is not) and, more importantly, is unpronounceable by me, therefore I have put some stretch of mental effort into memorising it.

As to the original question---What makes the title of a paper memorable?---, personally, when I look for things to read, my attention tends to be captured by titles that are short and sweet, for instance, Jean-Pierre Serre's *Trees*, Ken Brown's *Buildings*. These monographs/papers usually turn out to be the authorative treaties of the topics, with material unforgettable for one working in the field.


  [1]: http://www.springerlink.com/content/c935nx65v82r1001/
  [2]: http://www.math.washington.edu/~grunbaum/Your%2520polyhedra-my%2520polyhedra.pdf1.1.