A safe stimulant which is not caffiene does exist and it available as
a non-prescription drug from many health food stores. It's called
Dimethylaminoethanol, or DMAE. It works pretty well as a stimulant and
also increases levels of acetylcholine (it's a precursor). It also
makes rats perform significantly better on maze tests, because the
increased acetylcholine assists in some aspects of memory.

Another way to decrease need for sleep is to raise brain levels of
dopamine, which can be done by taking phenylalanine. It should be
taken on an empty stomach (500 mg to 1 gram is a reasonable dose)
with 1g vitamin C and 50 mg vitamin B-6 to assist in the conversion of
phenylalanine to dopamine. Another way to take the phenylalanine
is to place a small amount between the upper lip and gum about halfway back
in the mouth. There are blood vessels there which go directly to the brain.
If you're using this method, you should try a smaller dose (100 mg), as it is
more effective when taken in this manner.

Using these and other "safe" (i.e. adjusting the body's own chemicals
rather than introducing something new; not necessarily safe but a priori
a better bet than most traditional stimulants) I have been able to
cut my need for sleep by 4 hours per day without discomfort for weeks at a
time. I have no reason to believe that they would not be effective if
used longer, but circumstances of class work seldom required me to cut
sleep for longer periods than this.

Be advised, however, that these methods will not be as powerful as,
say, amphetamines or even high-dose caffiene, but they are not likely to
mess you up either. But if you are trying to stay up for two nights
to finish some huge project, you might be better off sticking with
caffiene and cold showers.