Hybrid HOV Waiver in Virginia
Note- if you already own a hybrid that you purchased before July 1, 2006, you can still drive HOV on 95/395 in Northern Virginia.
ALSO, someone mentioned a grandfather clause. In fact, as long as you have clean fuel plates before July 1, 2006, you can transfer them to a new eligible vehicle no matter when you buy it. It does have to be approved by Richmond, so your local DMV will have to fax your form.
I went round and round with the DMV after selling my 2003 HCH and getting a 2006 on July 26, well after the deadline, but I finally got my registration for my new car with the old plates.
If you want to check yourself, the law is listed on www.dmvnow.com.