Inspecting transactions:

# show me expenses for october (--period)
  ledger r Expenses -p oct

# what's the most expensive? (--sorted)
  ledger r Expenses -S amount --tail 10

# how much was spent on grocery? (--weekly, --monthly)
  ledger r Grocery
  ledger r Grocery -W
  ledger r Grocery -M

# what did I spend my Mastercard on? (--period, --begin, --end)
  ledger r mastercard
  ledger r mastercard -p "january"
  ledger r mastercard -b 01/25 -e 01/31

Graphing:

# Graph my bank account balance, monthly
  ledger r Savings -M

# Graph my expenses, monthly (-n = --collapse)
  ledger r Expenses -M -n

# ...what's the average per month?
  ledger r Expenses -M -n --average

Simple:

# what did I do yesterday?
# ..list transactions on this day
  ledger r -p 01/26
  ledger r -p yesterday

Switches:

# what's everything I got in USD? (--exchange)
  ledger b Assets -X USD