I've had no issues with Imation DVD-R.

The following is from the Wiinja site:

TDK DVD-R --> 16x -- PERFECT
XTRA DVD-R -> 8x -- PERFECT
IMATION DVD-R --> 16x -- PERFECT
VERBATIM DVD-R --> 16x -- PERFECT
VERBATIM DVD+R --> 4x -- PERFECT (Burn it DVD-ROM BOOTYPE)
EMTEC DVD-R -->> 4x -- Produces DRE on WII and Gamecube Modes
PLEOMAX DVD-R --> 16x -- PERFECT
PRINCO DVD-R -- > 4x -- Not Good Perfomance