Another option that I've heard good things about is the Tantus Suction Cup (link
), which slides in a standard vibrator pocket.
Other than that most suction cup bases seem to be either too weak and tear or too strong and have problems sticking to anything but the most smooth surfaces (Fun Factory suction cups do this. When they stick they're solid, but any little surface irregularity and they pop off).
Putting a little petroleum jelly on the suction cup (provided the dildo is silicone) will help things stick sometimes.