I have a 1998 Saturn SC1 (Manual Trans) that I purchased new.  I've put 105K miles on it and I have not had any trouble with it with the exception of a clogged fuel filter.  I have the oil changed on time every 3000 miles, but have not had any other mechanical maintenance done.  Should I have anything done or wait for something to break?

Maybe change the timing belt...

Sean

+1 they are chain driven

if you haven't already, change the serpentine belt and toss some fresh plugs and wires in there and you're good to go.

Plugs and maybe wires.
Flush the brake fluid.
Power steering fluid.
Radiator fluid.
When my civic reaches 100K I'm going to change the timing belt, but also the water pump belt and the ac or power steering (can't remember),  basically all of them while the timing belt gets changed.  Gives me a better piece of mind on longer road trips, cause I sure as hell wouldn't want to blow one out 400 miles from home.
Change your AC filter.  Mine is located under the glove box and it was so full of crap I couldn't believe it after 85K  Bugs, leaves, i believe it was white at one time, it was totally charcoal black when I took it out.
Might also want to change the air filter ever 20K if you dont' already.
MT/AT fluid.