If your username for gmail is user@gmail.com ...
Now if you want to use ebay with that address, use user+ebay@mail.com Now all mails will come in, pre-tagged for bins. They've done your work, for you.
Edit: its also good for finding out who's sharing addresses without your consent.
And besides, many sites that are necessary for doing business think luke+priceline@somewhere.com is an invalid email address. (And all of Priceline's competitors agree, and Kayak/Hipmunk are meta-search engines so don't solve the problem.)
That said, Priceline does allow you to unsubscribe from their marketing and only receive relevant emails, which is probably the ideal place to attack this problem.
there could be also some other mechanisms (filtering titles?) - come on, I'm sure there are solutions that won't require me to get through four separate screens and interrupt my workflow!
Maybe just archive them when you are in the middle of workflow, then have a weekly time when you work up filtering for the non-spam unwanted email you got that week.
The priority inbox feature seems like it was made for you as well.