Some tags I’m missing: rust, haskell, git, svn, cvs, mercurial, darcs, bazaar, vcs (version control in general), racket, c#, f#, erlang, d, ocaml, sml
Some architecture-specific tags: x86, arm, ppc, ia64, mips (mostly relevant for low-level hackery and assembly)
Some OS-specific tags: linux, solaris, aix
Some random tags: parallelism, concurrency, debugging, build (for build systems and such), osdev (operating system development)
Also, I strongly urge you to create c++ and obj-c tags. Trust me, most C programmers are not interested in C++ and vice versa.
Also, it is unclear whether the design tag is about software design, UI design, web design, …