Ruby 207 213 211 210 207 203 201 200 chars
An improvement on Anurag, incorporating suggestion from rfusca. Also removes argument to sort and a few other minor golfings.
w=(STDIN.read.downcase.scan(/[a-z]+/)-%w{the and of to a i it in or is}).group_by{|x|x}.map{|x,y|[-y.size,x]}.sort.take 22;k,l=w[0];m=76.0-l.size;puts' '+'_'*m;w.map{|f,x|puts"|#{'_'*(m*f/k)}| #{x} "}
Execute as:
ruby GolfedWordFrequencies.rb < Alice.txt
Edit: put 'puts' back in, needs to be there to avoid having quotes in output.
Edit2: Changed File->IO
Edit3: removed /i
Edit4: Removed parentheses around (f*1.0), recounted
Edit5: Use string addition for the first line; expand s in-place.
Edit6: Made m float, removed 1.0. EDIT: Doesn't work, changes lengths. EDIT: No worse than before
Edit7: Use STDIN.read.
