Minimum number of transactions so everyone has paid the same
Python, 308 Characters

I chose not to go after the bonus because the last time I used VB was over a decade ago, and I am still suffering from the PTSD ;-)

I didn't try and golf this very much because I'm not sure if that's the goal.  This code is guaranteed to return a solution with the minimum number of transactions.

def t(p):
 a=sum(p)/float(len(p))
 q=[([],p)]
 l=len(p)
 r=range(l)
 while q:
  n=q.pop(0)
  g=1
  for i in r:
   d=n[1][i]-a
   if d&gt;0:
    g=0
    for j in r:
     if n[1][j]&lt;a:
      v=min(d,a-n[1][j])
      y=list(n[1])
      y[i]-=v
      y[j]+=v
      if i!=j:q+=[(n[0]+[(j,i,v)],y)]
  if g:return n[0]


Usage

The t function takes a list of the amounts that each person paid.  Using the example from the question:

&gt; print t([50,25,5,0])
[(2, 0, 15.0), (3, 0, 15.0), (3, 1, 5.0)]


So the solution is for person 2 (George) to pay person 0 (Dave) $15 and for person 3 (Barry) to pay 0 (Dave) $15 and also to pay 1 (John) $5.