てぃーびーさんのずんだの1桁足し算問題をBrainf**kで実装しました。
ループの制御、複数桁の数字管理等、Brainf**kの初～中級として手頃な問題ではないかと思います。

実装(367文字)

** ずんだの1桁足し算問題
** prepare symbol characters
+++[->+++++++<]
>[->P++>E+++>C++++++<<<]
>P+>E-->>

** double loop
i+++++++++[-
 >>j+++++++++[-
  ** main
  * memory layout: PECi_j
  *  P E C: character code for PLUS EQUAL TILDE respectively
  *  i j: loop counters from 8 downto 0

  ** create several numbers from i j
  <<i[->+>>S->>I->>S-<<<<<<<]>[-<+>]
  >j[-<+>>S->>>J->S-<<<<<]
  ++++++++++[->S++>>I+>J+>S++<<<<<]

  * memory layout: PECij_S_IJS
  *  I J: 10 minus i/j
  *  S  : I plus J

  ** divide by 10
  >>>>>>>R++++++++++<<S--[->>R-[<r+>>>>]<[r+[->R+<]>>q+>]<<<<]

  * memory layout: PECij_S_IJ_rRq
  *  r q: remainder and quotient ( result of the division )
  *  R: 10 minus r

  ** digit compaction and replacement
  >>>q[+[-<<<+>>>]<R[-]<r+>>]  ( if q is not zero )
  <R[[-]<r+[-<+>]>]            ( else             )

  * memory layout: PECij_S_IJD(D)
  *  D: created digit(s) of S minus 2 through the division
  *  notice: I J D are all larger by 1 than they are meant to be

  ** convert numbers to characters and print
  <<<<<<S<++++++[->>>I[>]<[++++++++<]<<]
  >>>I-.<<<<<<<<P.>>>>>>>>>J-.<<<<<<<<E.>>>>>S--[-<<<<T.>>>>]>>>>D[-.>]

  ** print newline and clear temporary characters I J D then move j back
  ++++++++++.[[-]<]<<<[->+<]
 >j]
<<i]

実行例はideoneでの実行例を、Brainf**kの組み方についてはBrainf**k講座(リンク)をご参照ください。