SiteTagger includes an auto-complete feature for tags. This feature works in the tags field of the bookmark editing sheet and when adding tag filters in the collection editing sheet.
To use auto-complete, begin typing the first few letters of your tag and then press the option-esc key combination or the F5 key. A small list should pop up at the text insertion point with a list of tags that include the first few letters that you’ve typed. Use the arrow keys or the mouse to select the tag that you want. You may type while the list is open to further refine the list.