We have many many more than 5. From a neurobiological and functional point of view, touch comprises several completely distinct senses, including vibratory sensation, light touch, and pain/temperature. Proprioception is a major sense -- it's the sense of where a part of your body is in space. It's how you know that your arm is above your head without looking at it. Balance is a complicated sense that detects whether your head is upright or not, what direction you're moving in, and if you are accelerating. There are many visceral sensations that you can be consciously aware of (visceral means specifically with reference to internal organs), like hunger, nausea, distension of the stomach or intestines, distension of the bladder, and irritative processes in the lungs or airways. All these things are neurologically different.
Finally, there are sensory processes that you're not aware of that are critical for your body to actually remain alive -- like sensation of oxygen tension, acid/base balance, blood pressure, and many others that allow the body to self-regulate.
Given Theaetetus' agreeance with you, maybe there is more to your post then I was willing to give it.
For my (albeit limited) definition of senses, they have to be something we could be consciously aware of. Although we are not always reflective of what we see/feel/hear/smell/taste, when asked to comment on any one of those five we are able to elucidate what that sense relays (to varying degrees of success).
Your list raises two concerns for me:
1) How different are these sensations from the standard 5? To take an example, "Balance is a complicated sense that detects whether your head is upright or not, what direction you're moving in, and if you are accelerating." To what degree can we talk about balance without talking about the sensation of touch/feeling? I am not sure how balance would be possible without the sense of feeling: you 'feel' yourself moving towards one side or another, forwards or backwards, or accelerating in one direction or another. Just as an example, I cannot see how this would be seperate from how we feel within a space: acceleration is noticed because of the force we feel that holds us back, and possibly the air resistance we feel. Balance does not seem to be distinct from feeling, although a very strange use of it to be sure. This is something I see with many of the senses you offer, they all seem to be rooted in the other senses rather than in themselves as separate.
2) Is it possible to communicate these senses? This for me seems to be a large part of what we consider a sense. You mention several candidates for sensory processes which we are not aware, such as pH balance, which I would not rush to consider senses. If we are not aware of it, then how would we qualify it as a sense? I understand the body responds to it, accomidating for various homeostatic processes int he body without our consciousness of it (except in very strange cases, such as diabetics and insulin balance in the blood). However, I feel without consciousness of it, the ability to experience it as a perception, then it wouldn't qualify as a sense.
Perhaps we need a more rigerous definition of what we will call a 'sense'? My limited knowledge lends me to accept a more common-place definition, but this is apparently incapable of accepting alternatives. Aedes, have a better place to start for a definition?
(Which seems strange: all I sense is cold and a need for grain.)