Interestingly enough this is most often the case with pure mathemetics: their proofs are pursued purely in the interest of understanding & attaining them - the implications & applications of which are sometimes unrealized for decades (a great example is Evariste Galois: his number theory and symmetry/group work was decades-later applied by physicists to define many of the laws physics appear to obey - check out the wiki).
Or a certain obscure piece of algebra discovered by one G. Boole.
(Edit: During his time, Boole's results were practically unknown except to other logicians, and certainly nobody expected to find any practical use for them. It wasn't until the 1930s when Claude Shannon realized that the algebra that now carries Boole's name could be used to analyze digital electric cirquits.)
