Etsy, Paypal, and other online services you're likely to use in your business have the option to download CSV (comma-separated value) files. These files can make keeping up to date with your accounting much easier. You can use them by opening them in your spreadsheet software of choice.

Tip: Download the CSV for each month and name the file clearly like paypal-01-09.csv for the paypal csv for January 2009.

Open Office Calc - Open source spreadsheet software equivalent to Microsoft Excel but free.
Spreadsheet Basics - Open Office Tutorial
Google Docs - Online spreadsheets
Streamline Your Records with PayPal and Excel - Paypal specific tutorial, adaptable to spreadsheet software other than Excel