David,
I, for one, do not care for titanium knives. Mission makes the best Ti knives available but...they are still titanium. They tend to be difficult to sharpen AND do not seem to hold an edge well, an odd combination of traits. You will find that they are quite expensive also.
I think a reasonable choice would be one of the Voyagers from Cold Steel. Lots of options as far as size, blade shape and serrations. The AUS-8 steel they use is pretty stain resistant and the Zytel handle is more or less impervious to the effects of salt water. They do not have any washers at the pivot to get "gunked up" with sand/debris. They are easily found on the net at very reasonable prices so you will probably not get too bent if your knife ends up on the bottom of the ocean like dive knives have a tendancy to do.
If you really want to spend some cash on a dive knife, go for the Sebenza.
Hope this helps,
Derek