Verbatim is a good choice for most, but unless you are certain that your blu ray burner and [B]all[/B] of the playback equipment you own is compatible, you should stay away from their LTH line of disks. The LTH disks use organic dye rather than the usual inorganic recording layer. Here is an example of the regular Verbatim that will certainly work: http://www.rima.com/prod/96769.html
Recommending a site to buy them from is a little difficult since we don’t know which country you live in. If you are in the US, look at Newegg.com, Amazon.com, Rima.com, Supermediastore.com, and I"m sure there are many others. I usually wait for a sale.
Most commercial blu ray movies will not fit on a single layer blu ray, and the double layer blank blu ray disks are very expensive still. Do you know how to compress blu ray to fit single layer disks?