I recommend Verbatim. Burned over 1000 DVDs in the last year or so and the only coasters I have created using Verbatim occured when my old Sony burner was dying; can't say the same for the other brands I have tried.
I order from newegg.com; pay around $30 for a spindle of 50 and normally receive them w/in 3 business days.
You might also want to check Shop4Tech.com for blank media, inserts, and cases.