Minimal Boggle-like Arrangements
Python 342 355 398

R=(-1,0,1)
A=[];b={}
def s(w,x,y):
 if w: # not at the end of the word yet?
  for I in R: # search adjacent squares
   for j in R:
    if I|j: # skip the square we are on
     i=I+x;j+=y;c=b.get((i,j)) # get square in board
     if c==w[0]:s(w[1:],i,j) # square is what we are looking for?
     elif not c:b[i,j]=w[0];s(w[1:],i,j);del b[i,j] # we can set square?
 else:A.append(dict(b)) # all solutions
s(raw_input(),9,9) # run the search
A=min(A,key=len) # A is now the shortest solution
C=sum(map(list,A),[]) # put all board coords together
C=range(min(C),max(C)+1) # find the board biggest square bound
for r in C:print"".join(A.get((c,r)," ") for c in C)


Indent at four spaces is actually a tab character.

AMANAPLANACANALPANAMA:

MC 
NA 
PL


MISSISSIPPI:

S  
SI 
PPM


Oklahoma!:

oh    
 ma   
 ! l  
    k 
     O


Llanfairpwllgwyngyll is lethal ;)