How do I determine what pieces of vinyl siding to buy?
If you can remove one panel carefully you might find the manufacturer stamp on the back. It will narrow down the search down a little bit. Otherwise just a small sample would be nice to have when visit the stores. I've seen websites on the web that identify manufactures based on the sample that you send. Both Lowe's and Home Depot sell some vynil siding. Not a huge selection.

Honestly, it doesn't have to be exactly the same. The previous owner used a similar siding on the addition and i didn't notice until i had to replace a panel.