• Here’s a presentation about Agreeing & Disagreeing, the use of Connectors, Reactions, and Time fillers in Spoken English:
  
  Alternatively, you can download the PDF file here.
• Then there’s this presentation with useful Agreement&Disagreement vocabulary for Written English:
  
  Alternatively, you can download the PDF file here.

Take a look at this WebPage on the use of either & neither.

• EXERCISE:
  • Check this gap-fill exercise on Expressing Agreement.