If you simply mean huge amounts of spiritual power, then many characters have it. The highest currently would be Sōsuke Aizen, Ichigo Kurosaki and Genryūsai Shigekuni Yamamoto. If you meant the vast reiatsu defenition on Bleach Wiki, then only Ichigo and Zaraki have it. Vast is define as a huge amount of reiatsu that the person has little/no control over, ala Ichigo and Kenpachi.