Electronic dictionaries: Kanji Lookups
The most common Kanji Dictionary found in Electronic dictionaries is the Kanjigen 漢字源 followed by the Kangorin 漢語林
Methods of searching for a kanji:
You can search by pronunciation of the kanji (probably don't know it), pronunciation of the radical (probably DO know it since the pronunciation of the radicals are usually the radical's kanji's form's pronunciation.), by stroke number, by searching from a list of radicals and a few numbering methods.
Combining 2 or more methods greatly reduces the number of hits.