A File Icon — extra icons to identify different file types, small but useful
CodeMap – code tree representing the code structure of the active view/document
Markdown Code Blocks – add Markdown syntax highlighted code blocks, like in GitHub
MarkdownLivePreview – rendered live preview of your markdown doc in a new tab
SideBarEnhancements – enhances the options for Sidebar items (Files and Folders) by providing actions such as move to trash, open with..., or copy and paste
SyncedSideBar – sync the sidebar (folder view) for projects to highlight the currently active file view
TabsExtra – adds sticky tabs, fancier tab closing options, and other additional context-menu items for tabs
Workflow Utilities and Formatting Tools
AlignTab – quick alignment of list entries (i.e. align on ':' or '=>' or whatever)
Chain of Command – allows chaining of commands on a single hotkey (basically means custom macros)
FlowTree – automatically build a diagram of the files you open and why you open them
Hooks – run Sublime commands on common event hooks (e.g. on_new, on_post_save); super useful for automated workflow management such as SSH file-management.
Indent XML – automatically reindent / prettify XML and JSON
KeybindingHelper – simplify creating / checking key bindings via a helper panel that shows you useful info; very useful for customizing your ST3
MultiEditUtils – additional enhancements to multi-cursor selection; bit difficult to get the hang of, but very useful
Origami – provides shortcuts to split your current window into arbitrary panes (vertical and horizontal divisions), similar to tmux; very useful for quickly comparing files
ReIndent – utility to quickly convert convert an open file's indentation between spaces and tabs, or to change the indentation size
Text Pastry – additional tools for multi-select; modify selections, insert numeric sequences, incremental numbers, generate uuids, date ranges, insert continuously from a word list, and more
tabr – automatically select and tab between items in any list context (e.g. useful for quickly generating repeated fields with minor variations)
xpath – easier cursor navigation of XML and HTML files using XPath
IDE Integrations and Language Tools
LSP – Language Server Protocol support for ST3 that gives you IDE features; this is probably the single most powerful plugin in Sublime!
All Autocomplete – extends Sublime autocompletion to find matches in all open files of the current window
Build System Input – extends default Sublime Text 3 build systems to allow dynamic inputs through an 'args' panel
Jedi Syntax – syntax highlight plugin using the Jedi templating langauge; I'm iffy about the usefulness of this one…
LanguageTool – proof-reading and grammar checker for English, French, German, Polish and 20+ other languages; useful for actual text editing
PackageDev – tools to ease the creation of snippets, syntax definitions, etc; highly useful if you want to edit / create packages