'Arl's All Around

Even though it doesn't really lend itself to many nicknames, the "-arl-" sound seems to be on the rise, especially for girls (Charlotte, Charlie, Scarlett, Marley, Harley, Marlowe, Harlow). And there are so many more fun possibilities!
[yes, multiple forms of Charles/Carlos/Carla/Charlotte belong on this list, but there are just so many that I'm only including the really rare ones]

Boys:

• Arlen (AR-len, English)--origin unknown, poss. from Erlend (Norse, "foreigner"), Harlan (Old English, "hare-land" or "hard land"), or Erlwin (Old English, "earl-friend"). Also spelled Arlan.
• Arlind (ar-LIND, Albanian)--"gold-born".
• Arlindo (ar-LIN-doo [short 'oo', like "foot"], Portuguese)--masculine form of Arlinda, prob. from Erlinde "army-shield", or similar Germanic name
• Arlo (AR-loh, English)--from Irish place name Aherlow, prob. "between two high lands", or poss. a form of Harlow (Old English, "army hill" or "rocky hill")
• Carlin (CAR-lin, English)--from Irish surname O'Caireallán, prob. "little warrior". Also Anglicized as Carlan or Carlon.
• Charlot (shar-loh, [archaic] French)--diminutive of Charles. Another form was Charlon (shar-lohn).
• Carlton (KARL-ton, English)--from Old English "freeman-town". Another form is Charlton (CHARL-ton). 
• Garland (GAR-land, English)--from Old English, "triangle land" or "crown, wreath"
• Harlan (HAR-lan, English)--from Old English, prob. "hare land" or "hard land". Also spelled Harland.
• Jarl (YARL, Scandinavian)--"chief". Another form is Jarle (YAHR-leh, Norwegian).
• Karlis (KAR-lis, Scandinavian)--form of Charles. Another form is Kārlis (KAR-lis [rolled R], Latvian).
• Karlmann (KARL-mahn, German)--"freeman"
• Marlon (MAR-lon, English, German, Scandinavian)--origin unknown, poss. a form of Merlin (English, "falcon"), Marcelin (French, diminutive of Marcel/Marcus), or Marland (Old English, "moorland")
• Varlam (VAR-lam, Russian)--form of Barlaam. Also transliterated as Varlaam.

Girls:

• Arla (AR-lah, Scandinavian)--short form of Arnlaug "eagle-promised" [also means "early" in Swedish]
• Arlette (ar-LET, French)--form of Germanic Herleva, poss. "army battle" or "noble battle"; or similar Her/Earl-name.
  Other forms include Arlete (ar-LEH-teh, ar-LEH-chee, Portuguese), Arletta (ar-LET-tah, English) and Arleta (ar-LEH-tah, Polish, Scandinavian).
• Arlinda (ar-LIND-ah, Albanian)--feminine of Arlind, "gold-born"
• Arlinda (ar-LIND-ah, English, Portuguese)--prob. from Germanic Erlinde "army-shield" or similar
• Arline (ar-LEEN, English)--origin uncertain, poss. from the English surname Arline (prob. from Erlwin, "earl-friend", or similar Erl-name) or an invention based on names like Charline and Arlette. Also spelled Arlene or Arleen.
  Other forms include Arlene (ar-LAYN, Swedish; ar-LEH-neh, Norwegian, Finnish), Arlène (ar-LEN, French), and Arlina (ar-LEEN-ah, English, Spanish)
• Carlijn (KAR-line, Dutch)--form of Caroline. Another form is Carlina/Karlina (kar-LEE-nah, German, Scandinavian)
• Darlene (dar-LEEN, English)--from English word 'darling'. Also spelled Darline or Darleen. Another form is Darla.
• Jarla (YAR-lah, Icelandic, Swedish)--feminine of Jarl, "chief"
• Marla (MAR-lah, English)--short form of Marlene/Marlena
• Marloes (mar-LOOS, Dutch)--contraction of Maria Louise
• Marlis (MAR-lees, German; mar-LEES, Dutch)--contraction of Maria Elisabeth. Also spelled Marlies.
• Sarla (SAR-lah, Hindi)--from Sanskrit, "honest, straight"

Unisex:

• Arlie (AR-lee, English)--from Old English "eagle-meadow". Also spelled Arley or Arleigh.

There are also tons of surname and place-names (mostly Old English), that fit the bill (like the modernly-trending Marlowe, Harley, Harlow, Marley, Charleston, etc), for almost every letter of the alphabet. :p

• Arliss / Arlosh
• Barlow
• Carlyon / Carleon
• Carlow
• Darley
• Darlow
• Darlton
• Farlam
• Farley / Varley
• Farlow / Varlow
• Garley / Jarley
• Parley
• Sharland