Do you mean a scanner or a laptop to run WinALDL?
'Scanners' are either cheap and basically just read codes, which you can do from your SES light anyway, or they are expensive ones like a tech would use. These ones are by far the best but very expensive. WinALDL run from your laptop is very useful as are several other programmes, but it's free!
What problems do you have? Have you read the SES?