While it's quirky in its search functionality and sometimes slow, Starostin's Etymological databases (
link) has Pokorny's
IEW (Indogermanisches etymologisches Wörterbuch) digitized and searchable. I have the brick & mortar version, but I still sometimes use his site when away from the home library. Watkin's root dictionary (part of the AHD4) always give the page number of the
IEW for corss-reference purposes. (It's also availabe as a small booklet separate from the dictionary. The IEW also covers PIE roots that have no English reflexes. Starostin also has other dictionaries online, like Vasmer's Slavic etymological dictionary.
