Other than going fully academic and getting a doctorate/post-doc, or going for a more or less 'standard' job in software development, what are some other career options in the full or semi theoretical C.S field?
Assuming you do not get intimidated when reading theory papers due to your training in your master's degree, which I assume is in a theoretical aspect of CS since you are asking on this site, I think it would be a great idea to try being a research programmer (usually inside some research organization, like an industrial lab or under the umbrella of a larger grant).
Why? It's not easy to implement an algorithm correctly, even if the authors sincerely meant to spell it out completely, and yet sometimes the need to run an algorithm does arise! Additionally, if you enjoy programming and measurements, later on you may even be able to further your study into a PhD in the area of algorithmic engineering, which I think is a very exciting area and wish to see more of it happening. (Check out the ALENEX conference and the DIMACS implementation challenges.)
Any "cutting-edge" technology field will look for theoreticians.
Are you familiar with the teachings and lore of SICP, PAIP, TAOCP? Do you know why monads really are like burritos (or have an even better analogy)? Do you have a love/hate (or just love?) relationship with Hindley-Milner inference? And can you make code run so fast your CPU begs for mercy? Then we want to talk to you.
It goes on to guarantee a phone interview to anyone who has solved P != NP (amongst other things).