You can find out how much your steam account is worth with this. It calculates the total of your account as if every game was bought separately and at the current price.
  
This is what my account is worth:
MonkeyGekko 
Found 76 Games with a value of 
$1131.25 USD
 
As a fun comparison. This is what Brad's account is worth: 

Rudds  
Found 538 Games with a value of  
$8830.69 USD    

My steam Id never works, what do I have to do again?

 Found 35 Games with a value of $519.66 
 
I usually buy games when they are on sale.

" @Whisperkill: You've to change your privacy settings to public.  Just a heads up to everyone. It won't show the price if you c/p it in for some reason. "

61 games / $849.42 
 
I was expecting more for some reason.

a lot

$19.99
 
fuck my life

  
 
$244.87usd  
 :(

 Found 13 Games with a value of  
 
lol I've only spent $13 total on steam.

28 games = $304.76
 
I buy most of my games when they are on sale.

I...I don't want to know.

found 111  games with a value of ...   
 
   1891.92 USD 
 
 but i have 140 games. soooo

missing 10 games for some reason  but it is worth  $ 834.64

It says my account is worth $119.93, but I haven't spent that much on Steam.  With all the sales included I've only spent like $33 or so on Steam.

 Found 4 Games with a value of  $84.96 USD 

Cobbe354
 
Steam member since: 2008-10-10
Found 11 Games with a value of  $139.90 USD.
 
Oh well. I don't play PC games that much anyways. Garry's Mod and Counter Strike would be the only ones I'd play really.

$1079.46 though I noticed there were a couple games that weren't counted... 

 Found 13 Games with a value of  
 
I rarely ever use steam.

" @Ryax: I assume that your profile says you have 140 right? You can't count on that, if that is the case, because it also counts some SDK programs, and a few games are counted twice, like MW2. My profile says I have 96, but I only have 76. "

 Found 18 Games with a value of  $289.82 USD
Nifty site, but it's overshooting a bit because any sane person would get Orange Box as a package.
 
In reality, I spent roughly $61.50 - every game I bought was on sale. Good stuff.

About $300 according to that calculator, but I've spent around $50 thanks to sales.

24 games, $384.78.  In reality though, with all the sales, I probably only spent 180.

I don't like to think about all the money I dump into Valve's wonderous game dispenser. Ignorance is bliss.

 Found 12 Games with a value of  $219.89 USD  That's what I was guessing it was worth too. 

Found 44 Games with a value of $713.57 USD 

56 Games.
 
Worth...$943.45 USD 
 
And I've only bought on sale stuff, so I've spent a fraction of that.
 
Edit: Not counting 3 Demos and the R.U.S.E. beta I assume.

196 Games - $2677.07 USD

 Found 80 Games with a value of  $1204.20
 Wow I thought I had more than that.
 
Heh heh... $4.20

Found 42 Games with a value of  
I'm surprised it's that much, considering the fact that this is a new steam account I started buying games for just last July.

10 games,  $ 179.90. 

 Found 9 Games with a value of $189.92 USD 
 
I have only actually spent about 120. Everything else was on sale.

 Found 17 Games with a value of  $219.83 USD 

35 Games for $744.65. I don't think I've even spent $200 though. Also, I think I've only played about 6 of them.

62 games at $782.42.  I definitely haven't spent that much on Steam, but this site doesn't take into account sales prices. In total I probably spend about $250-300 for all of my Steam games.

"Found 54 Games with a value of $979.47 USD."
I guess I should start playing some of those now. I bet the numbers are way higher than they should be, considering I bought that $50.00 THQ Complete pack last October.

There's already a thread about this. Two, I think.
 
Anyway, $1764.03 USD 

 Found 180 Games with a value of  $2444.19 USD 
 Oh Steam, I love you so..
 
edit: Also I have well over 200 games but I guess it counts them as bundles?

$813.44 USD 

Found 540 Games with a value of
$8860.68 USD
Take that Brad!

 Found 25 Games with a value of $294.76 USD 

New update. It's up to $620.65 USD