I love Jeremiah 29:11 too! And here's another great one when you are in those times where it's so painful and it's hard to express to God how you feel. I've been in those times too, and this is one of my favorite scriptures to remember in those times. Sometimes I believe silent prayers are all that's needed, as we depend on the Holy Spirit to speak for us:
Romans 8:26
Likewise the Spirit helps us in our weakness. For we do not know what to pray for as we ought, but the Spirit himself intercedes for us with groanings too deep for words.