- Awwwards
- The FWA
- Unmatched Style
- Subreddits
- Web Top Source
- freepik
- UI Kits
- Phantom Open Emoji: A completely free and open set of emoji. Use and distribute with any project!
- The Stocks
- picjumbo
- Gratisography
- Unsplash
- Little Visuals
- Death to the Stock Photo
- Superfamous (requires attribution)
- Life of Pix
- IM Creator
- Getrefe
- Jay Mantri
- New Old Stock
- The Pattern Library
- IM Free (requires attribution)
- Public Domain Archive
- Magdeleine
- [Foodiesfeed](http://foodiesfeed.com
- Picography
- Raumrot
- ISO Republic
- FontAwesome
- Ionicons
- Noun Project
- Round Icons (Paid, free 60 icons)
- Mega Flagship (PSD, AI, SVG, EPS, SKETCH)
- Typespriation
- Beautiful Web Type
- Beautiful Web Type Combinations
- slabText - jQuery plugin for producing bold and responsive headlines
- PrepBootstrap (widgets and themes)
- Bootsnipp (snippets)
- Bootstrap Taste
- Bootswatch
- Start Bootstrap
- BlackTie
- Designmodo's flat-free and Startup Framework are pretty cool.
- BootBundle(no idea what this does)
- Bootstrap Stage
- Bootstrap Zero (widgets and themes)
One of these upgraders might actually work for you (or reduce your work) when going from v2 to v3: This, this, or this.