One of the biggest issues I have found is how to keep track of your transactions as well as calculate the value of your portfolio. I have tried countless programs over the years and none have really given me the flexibility to add the details and features I want. A number of years ago I came across this excel worksheet which I modified and updated to work with Yahoo's UK site, (I believe the worksheet originally came from the Motley Fool UK website). It is in Excel 2003 format and you will need to allow it to run macros to update prices etc. It should be relatively easy to modify this for use in other markets - use alt+F11 to view the code behind the worksheet.
In order to use the sheet you need to enter your trades in the 'Trade' tab and then just enter the corresponding stock code in column 'A' of the 'Current' tab. When you hit the 'Get Prices' button it will update all records on the sheet.
I have placed some example stocks on the sheet to show you how it works and what data you will need to input. This is a very versatile and easy way to maintain your portfolio as well as to keep track of your trades.