JavaScript 1.8 (SpiderMonkey) - 354
x={};p='|';e=' ';z=[];c=77
while(l=readline())l.toLowerCase().replace(/\b(?!(the|and|of|to|a|i[tns]?|or)\b)\w+/g,function(y)x[y]?x[y].c++:z.push(x[y]={w:y,c:1}))
z=z.sort(function(a,b)b.c-a.c).slice(0,22)
for each(v in z){v.r=v.c/z[0].c
c=c>(l=(77-v.w.length)/v.r)?l:c}for(k in z){v=z[k]
s=Array(v.r*c|0).join('_')
if(!+k)print(e+s+e)
print(p+s+p+e+v.w)}
Sadly, the for([k,v]in z) from the Rhino version doesn't seem to want to work in SpiderMonkey, and readFile() is a little easier than using readline() but moving up to 1.8 allows us to use function closures to cut a few more lines....
Adding whitespace for readability:
x={};p='|';e=' ';z=[];c=77
while(l=readline())
l.toLowerCase().replace(/\b(?!(the|and|of|to|a|i[tns]?|or)\b)\w+/g,
function(y) x[y] ? x[y].c++ : z.push( x[y] = {w: y, c: 1} )
)
z=z.sort(function(a,b) b.c - a.c).slice(0,22)
for each(v in z){
v.r=v.c/z[0].c
c=c>(l=(77-v.w.length)/v.r)?l:c
}
for(k in z){
v=z[k]
s=Array(v.r*c|0).join('_')
if(!+k)print(e+s+e)
print(p+s+p+e+v.w)
}
Usage: js golf.js < input.txt
Output:
_________________________________________________________________________
|_________________________________________________________________________| she
|_______________________________________________________________| you
|____________________________________________________________| said
|____________________________________________________| alice
|______________________________________________| was
|___________________________________________| that
|___________________________________| as
|________________________________| her
|_____________________________| at
|_____________________________| with
|____________________________| s
|____________________________| t
|__________________________| on
|_________________________| all
|_______________________| this
|______________________| for
|______________________| had
|______________________| but
|_____________________| be
|_____________________| not
|___________________| they
|___________________| so
(base version - doesn't handle bar widths correctly)
JavaScript (Rhino) - 405 395 387 377 368 343 304 chars
I think my sorting logic is off, but.. I duno. Brainfart fixed.
Minified (abusing \n's interpreted as a ; sometimes):
x={};p='|';e=' ';z=[]
readFile(arguments[0]).toLowerCase().replace(/\b(?!(the|and|of|to|a|i[tns]?|or)\b)\w+/g,function(y){x[y]?x[y].c++:z.push(x[y]={w:y,c:1})})
z=z.sort(function(a,b){return b.c-a.c}).slice(0,22)
for([k,v]in z){s=Array((v.c/z[0].c)*70|0).join('_')
if(!+k)print(e+s+e)
print(p+s+p+e+v.w)}
