G, D, G, B, D
The most standard 5-string banjo tuning. This is referred to as "Open G" Tuning because the banjo is tuned to an open G chord, meaning that if you strum the banjo without fingering any of the strings on the neck you will be playing a G chord.
G, C, G, C, D
Often used in Old Time music, this is referred to as "Double C" Tuning because the banjo has two C strings.
G, C, G, B, D
This is referred to as " C" Tuning. It can also be referred to as "Drop C" Tuning because coming from the open G tuning, the D string on the 4th string is dropped down to a C.
F# (or A), D, F#, A, D
This is referred to as " D" Tuning. If you strum the banjo without fretting any notes in this tuning you will be playing a D chord. Earl Scruggs used this tuning in his famous recording of the song "Reuben".
C, G, D, A
The most standard tenor banjo tuning. This is referred to as "Standard Tenor Tuning" for obvious reasons. This tuning is the intervals of fifths and is exactly the same as viola or mandola.
G, D, A, E
Referred to as "Irish Tenor Tuning". This tuning is also in fifths but is lower in pitch than the standard tenor tuning. This tuning is like a violin or mandolin, only one octave lower.
D, G, B, E
This tuning is the same as the top four strings of a guitar and is often referred to as "Chicago Tuning". This makes it very easy for guitarists to pick up a 4-string banjo and start playing.
C, G, B, D
The most standard plectrum banjo tuning. This is very close to the standard 5-string tuning (without the 5-string), but the 4th string is dropped down to C.
D, G, B, E
This tuning is the same as the top four strings of a guitar and is often referred to as "Chicago Tuning". This makes it very easy for guitarists to pick up a 4-string banjo and start playing.
E, B, E, G#, E
This is open E tuning. Really it is the same as open G tuning, just 3 steps lower in pitch.
E, A, D, G, B, E
This tuning is exactly the same as a guitar.
E, E, A, A, D, D, G, G, B, B, E, E,
This tuning is exactly the same as a 12-string guitar. To be more specific, this is the same as a regular guitar, but the low 3 strings are doubled separated by an octave and the top 3 strings are doubled in unison.