I've been using Ledger to keep track of my finances for several years, and one feature I really like is the ability to run reports from within Emacs via ledger-mode.

Creating these reports is done by customizing the ledger-reports variable. It's also possible to set them using the ledger-reports-add function, but I prefer to set them all in one go during setup.

My current list of reports looks like this:

(setq ledger-reports
 '(("bal"            "%(binary) -f %(ledger-file) bal")
   ("bal this month" "%(binary) -f %(ledger-file) bal -p %(month) -S amount")
   ("bal this year"  "%(binary) -f %(ledger-file) bal -p 'this year'")
   ("net worth"      "%(binary) -f %(ledger-file) bal Assets Liabilities")
   ("account"        "%(binary) -f %(ledger-file) reg %(account)")))
Shows the balance of all accounts; this also includes individual expenses (such as Expense:Car:Gas) so it's a pretty long report.
bal this month
As above, but only includes transactions from the current month.
bal this year
Same as bal, but limited to the current year.
net worth
A short report that shows what I've got in each account, as well as what I owe on loans and credit cards.
This prompts for an account name and then shows its transactions for the current file. This is useful for quickly seeing how much money has been spent on a specific category during the year.

Emacs reports that have the %(ledger-file) token are run against the current ledger file. I have my Ledger files stored in a projectile project so I can quickly jump to them to run reports or make adjustments.