Since the reader states that they own two Dobsonian telescopes with 8 and 10 inch apertures, there are several kinds of projects that would be difficult. Dobsonian mountings cannot be used to accurately track a star as it moves diurnaly. For this you need an equatorial mount and a clock drive. This means that you probably will not be able to do long-exposure photography to photograph faint nebulae or galaxies. You can, however, attempt a photographic atlas of the Moon which only requires exposures of a second or less.
Variable star studies are also extremely popular. Check out magazines such as Sky and Telescope or Astronomy for lists of candidate stars that might be of interest to monitor over the course of a few days or weeks.
Lunar occultations, or occultations of stars by planets is also a very interesting line of research. Many amateur astronomers are members of national and international networks who carefully determine the eclipse times using their telescopes and accurate time keeping clocks from various locations around the world. Contact a local chapter of an amateur astronomy society for more details. If you search YAHOO under amateur astronomy you will find many listed.
You can also try your hand at keeping track of features on Jupiter which change from week to week throughout the Jovian 12-year, year.