This post is for the benefit of non-Pioneer drive makes (mostly Sony but also DD0203 and NEC/TDK +/- 4x)
Princo 1x burned fine on my Pioneer 104, but they fail about 50% of the time on the Sony DRU-510A (or 500A, tried that too.) If you have a Sony, stay away from the Princo 1x media. DVD-Pro is Princo, so are some others (Leda, many storebrands, etc), check on DVDRHELP for disc codes that are princos. Basically Princo makes the cheapest of the cheap media.
Note: For both Ritek and Princo, there *is* a difference between 1x and 4x media.
The Princo 4x will also not burn at 4x on the Sony so stay away from that as well, unless you dont mind 2x burns. CMC Magnetics is hard to find unbranded, but they have a LOT of problems, so watch out for made in Taiwan TDKs and Verbatims (possibly Taiwanese Fujis too)
For cheap media on the Sony, you can try the LeadData 4x (or OEMs, such as Sony) or the Ritek G04 (or OEMs) which supposedly burn at 4x. Ritek is more expensive but not a LOT more expensive.
Keep in mind, you should be able to buy name brand discs on special or sale from time to time for under $2 each, the best 4xs are those made by MCC (Mitsubishi) in Singapore or Japan, the Ricoh discs and the Phillips, so if you find a deal on any of these especially in store where you can look at the Made in ... label, look out for those.
Hope that helps some people.