I use the humble Double Rectangle punch a LOT. In my opinion, it's a very worthwhile $11.50 investment!
Here are some of my favourite ways to use it: (number 2 is the promised Nifty Knot-Tying Tutorial)
1. Make Ribbon slots
2. Tie a nifty knot (*NEW* Tutorial)
3. Tie a Faux bow
4. Make an ornament hanger
5. Make a candy-cane sized hole