They split the oil into eight portions using only one eighth each night, yet each eighth lasted the entire night.
The first day is a celebration of winning the war while the rest of the seven were for the miracle.
They poured the entire contents of the jug into the menorah yet only an
eighth burned.
The miracle was that after filling the entire menorah from the oil in the jug, the jug still remained full.
There is an opinion that there wasn't even sufficient oil in the jug to light an entire night.
Eight miracles happened during Chanukah:
- G-d fought our battles
- G-d judged our Judgement
- G-d sought our revenge
- G-d delivered the mighty into the hands of the weak
- He delivered many into the hands of few
- The impure into the power of the pure
- The wicked into the hands of the righteous
- The vain into the hands of those who study His Torah.
The Talmud (Sabbath 21b) discusses the dilemma of lighting eight candles.
Shammai is of the opinion that you light on the first night eigth, second
night seven etc. Hillel is of the opinion that you light one light on the
first night, two on the second etc. 
Rabbi Judah Loewe (The Maharal of Golem fame) explains this argument in
the following manner. Shammai looks at the viewpoint of the miracle. In
terms of the miracle, the first day the miracle occurs has in it the source
for all the rest of the time the miracle lasts. Hence the miracle is at
its greatest the very first day, and then begins to wane. Hillel however
takes the viewpoint of the person observing the miracle. The person is
incremently affected by the miracle each moment it continues to occur,
hence the effect the miracle has on the person is the weakest on day one
and the greatest on day eight.