You can use 5 volts as one voltage, then use GND (0 volts) for another (assuming the 5 volt power supply is regulated).
Then you only need 6 more voltages equally spaced.
simulate this circuit – Schematic created using CircuitLab
The Output volts is calculated by : \$Vi*R2/(R2+R1)\$
Where Vi is the Regulated 5 v.
You can even use the circuit simulator to measure the Output volts.
Change R2 to obtain other values.
I selected R1 as 100K. You could use a R1 of even 1 Meg ohms to reduce current consumed.
I added capacitor C1 so that your Analog to Digital converter won't drag down the Output volts. The capacitor holds the voltage constant while the ADC does it's sample and hold. (EDIT 2 : C1 changed from 10nf to 100nf)
EDIT 1 : added note on sample and hold, per comment by RobbhercKV5ROB
Taken from Data sheet for the processor :
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is held at a
constant level during conversion.
EDIT 2 : I have changed the capacitor C2 from 10nf to 100nf to account for the following from the ADC specifications :
The ADC is optimized for analog signals with an output impedance of approximately 10 k or less. If such a
source is used, the sampling time will be negligible. If a source with higher impedance is used, the sampling
time will depend on how long time the source needs to charge the S/H capacitor, with can vary widely. The user
is recommended to only use low impedance sources with slowly varying signals, since this minimizes the
required charge transfer to the S/H capacitor.