1. Exactly. 2. Absolutely. 3. That's so true. 4. That's for sure. 5. I agree 100% 6. I couldn't agree with you more. 7. That's exactly what I think. / That's exactly how I feel. 8. (informal) Tell me about it! / You're telling me! 9. (informal) I'll say! 10. I suppose so. (use this phrase for weak agreement – you agree, but reluctantly) Note: Avoid the common error of saying "I'm agree" – the correct phrase is "I agree" or "I'm in agreement" – the second one is more formal.