If you find a listing that interests you, you can add it to your Want List.
This is on the listing under the Add To Cart button (don't use that! it means you are definitely buying!) on a small drop down menue called Add To List.
Chose Want List.
You will then be able to see the items that you have put on the list indefinitely. The Want List is kept under My eBay at the top right of your page.
You can even use the Want List to compare various similar items.