I just discovered this great program that runs on OS X.
Essentially, you tell it the tidal heights (or range) in which you are interested, the timeframe of interest, and it spits out an ics file (like iCal or BusyCal use) containing the dates, times, and tide info that fit those parameters.
So, say you want to perform a study that requires minus tides (<0.0m MLLW), and you want to do your sampling in April or May, and it needs to be done during the afternoon. You can simply give the program those parameters, hit "compute tides", and it will magically spit out a .ics file (or text file) that you can then use to plan your sampling dates. I can think of a ton of ways this could be great - trying to find specific tidal heights for sampling or tidepooling; planning trips to locations that require low tides for access; or making sure certain stretches of water will be navigable.