St Helena Stamps
The first Post Office was established on St. Helena in 1815, and the first handstruck stamp was introduced shortly after the opening of the Post Office. The first adhesive stamps of St. Helena were introduced in 1856.
St. Helena & Dependencies
Watermark varieties, plate flaws, major errors, perforation changes, shades, postage due stamps and booklets are all listed and priced.
Wikipedia page providing a brief overview of St Helena stamps and postal history.