Good stock footage of what?
Detonation films has some good stuff, as mentioned, but it is very limited in scope; they only offer pyrotechnic visual effects footage. If that's what you are after, take a look at http://www.nccinema.ch/eshop.html
Sollthar's HD effects packs as well, at No Control Cinema. Absolute premium quality at extrememly affordable prices.
There's an assortment of stock footage contained in the old AlamDV plug-ins
, for owners of FXhome software. it is of widely varying quality, but there is some good stuff.www.istockphoto.com
has stock footage in nearly every category you could want, as well as stock photography, for pretty reasonable prices.
And of course, the original and traditional way to get stock footage... film it, and stock it on your shelf. These days, more likely on your harddrive, but still. The trick to this is to film it when you don't necessarily need it, but when you have the chance. Then when the need arises, you have it in stock. If you bring your video camera along, any trip to the city, the countryside, the zoo, the ocean, or almost anywhere else can be an opportunity to increase your stock of footage for later use.