Useful Value Screen

I wanted to post a few useful screens I use at work to find stocks. One of the guys I work for is a real value oriented investor and I thought it might be helpful for investors who like value, to see the screen I use.
First, the website I use the most for screening is MSN. I think you have to download some software, but it's a great tool.
The parameters I use: Return on equity (ROE) greater than 10%, net profit margins greater than 5%, and debt/equity ratio of less than 0.70
This normally brings up tons of stocks, so I usually limit this list by using a 3 month relative strength number of less than 25.
For my example I will use Serono (SRA), which is one of the biggest biotech companies. This stock made it through my screens, and then the stock manager looked further into SRA (the screen is just a preliminary tool, you still need to do further research) when it was around $15/share. We took a position and it has since moved up a bit to the $17 range. I'm not promoting SRA or anything, I'm just using this as an example.
Okay so SRA made it through the first screen, now this is the other part.
I use the Key Statistics from Yahoo Finance
http://finance.yahoo.com/q/ks?s=SRA
and also the 10 Year Key Ratios from MSN

I re-check the ROE, profit margins, and debt/equit ratio. Then I look at insider holdings because the stock manager wants insiders to hold a good chunk of the stock. For SRA this is over 60%, I normally check out the percent but also take into account the total Market Cap of the firm. If insider holdings is 1%, but if the market cap is 70 billion, this is still a nice chunk.

The next thing I check is the average volume, because the firm I work for usually doesn't invest in thinly traded stocks.
I also limit the p/e ratio to less than 40.
Now on to the value part. If the stock is non-financial/insurance I look at their current price/sales ratio. If the stock is financial/insurance I look at the price/book ratio.
For SRA, we take a look at the current p/s and it's at 3.06 ttm (trailing twelve months)
I then compare this number with the 10 year p/s numers found on the MSN site.
I'm looking for a current p/s ratio that is on the low end of the 10 year ratios.
(It doesn't have to have ten years worth of data, it's just that the site is called a 10 year summary).
For SRA we see that over the past years the p/s ratio has ranged from 6.8 to 19.
So based on these measures, they seem to be undervalued. The next step is to look further into the company, ratio analysis, and check if the company is healthy. Certain stocks come up and appear to be undervalued, when they are having troubles- these, of course, are the ones you want to stay away from.
I think this screen does a fairly good job of finding undervalued companies. This is definitely not for growth investors and some of the parameters used can be changed. For instance, the insider holdings- at work my boss is conservative and he wants to see major insider holdings, but it's up to the investor when it comes to this parameter.