Take a look at the following

Documents to Go - lets you put Excel and Word Documents on your Palm.
MobiPocket - and electronic book reader (games only go so far as a time sink)
Books- Dictionary/Thesarus, fiction (science of course) Baen books has been releasing jam packed CD's in some of their hardbacks.
A more functional calculator. Your choice of many

Do the T's accept a flash chip? Buy the biggest available. Books average a meg each. (I have 2 dozen loaded now) Swapping is a pain, and you never seem to have the chip you want or even know which to look on.
They also make a handy way to backup the main memory of the palm itself. (I'm assuming the T is like my sonypda/memorystick where this is concerned)

Additional system fonts. (well maybe?) Depends on the resolution of the screen.
I have one font that is sharply readable but eyestrainingly small. That's more interesting than truly useful.