Links to Google Books and Archive.org for online versions of English-Persian dictionaries.
This is a sample of online English-Persian dictionaries. Search Google Books or Internet Archive for more, and for multiple editions of some of the books below. All Google links below used to give the entire book as a free download, but many are now only available as "preview".
Haim (below) was the Persian dictionary used in my university course, and Steingass is also a classic. [-J.W.]