The Locrian mode is useful for improvising over a half-diminished chord a.k.a a minor seventh chord with a flatted fifth. The half-whole scale might be a more exciting choice, though, eg., C Db Eb F# G A Bb C.

One can use mathematical methods to construct all sorts of scales, modes and melodic patterns. With computers nowadays, it's reasonably easy to do this and even to typeset them automatically. A classic book (and it really is a classic that deserves this overused epithet) on this subject is Nicholas Slonimsky's _A Thesaurus of Scales and Melodic Patterns_.

I could go on about this (and on and on), but I have to start work.