Presearing is amazing. Life is blissful and your character is ignorant of everything!
Just about anywhere:
"Group LF monk for mission"
"LFG Bonus only!"
"WTS <insert drop item nearby collectors want>"
"WTB <insert drop item nearby collectors want>"
In Lion's Arch:
"WTS Sigil 80k!"
"WTB Sigil 20k!"
"Selling my guild! Whisper with offer!"
"Running people to D'Alessio Seaboard 500g each! At henchman!" <-- I always laugh my ass off at this, it's just royal. The Seaboard is all of ten feet away.
"'<person with commodity>, why didn't you sell me <commodity>?!'
'Your bid wasn't high enough'
'OMGWTF <person with commodity> overprices! Don't buy anything from <person with commodity>!'"