For prospetive geek parents, here is the list of baby names that only contain the letters A B C D E F:

Ada
Becca
Bea
Eda
Fae
Cadee
Abcde
Dea
Febe
Bae
Edda
Adea
Dae
Bebe
Cece
Ebba
Edee
Cade
Ace
Abe
Dade
Efe
Dace
Dee
Cabe
Cace
Ab
Abba
Ed
Ac
Acea
Abed
Bae
Ebaad
Ebba

There are at least five kids born in the USA in 2013 who have these names, according to the SSA: http://www.ssa.gov/oact/babynames/limits.html

If you want leet-speak names, there are 120 of them:

Ad4
Abb13
Add13
A1d4
Ed13
Ac4c14
B3cc4
A01f3
B0bb13
C0c0
D14
B0bb1
Ac4d14
Ad14
Eff13
Abb1
A1d3
Ad1
C414
D3bb13
B0
C0d1
Add1
B34
Ed4
F14
C41
C0b13
C0d13
F43
C4d33
Ab1
Af14
Abcd3
C4d13
A1d33
C1c1
D34
Ab14
A01
D4c14
D4c13
A1
F3b3
B43
Edd4
Ad34
B1b1
B03
C3c14
C0b1
D43
A4d1
Ab1d4
Ad41
Ad1b4
B3b3
C3c3
D044
Ac13
Ad13
A14
C0d4
C0d33
D4c1
Ebb4
Ed33
Ed1
C4d3
Ac3
Edd13
B0
B0d13
B0d3
A4d1
Ab3
C41
F4b10
B03
C0d4
C410
D4d3
Ad1
B0d33
C0b3
Abd1
B0b
B40
B0d1
Ef3
C0d1
F4d1
D4c3
C0d13
D33
C0b1
C0b13
D0c
Ab1d
C4b3
C4c3
Ab
Abb4
C41d3
D30
Ed
Ac
Ac34
Ac13
Ad1b
C1d
C03
D10
Ed1
Ab3d
B43
C01
D4c0d4
Eb44d
Ebb4