When entering items into your bank accounts (checking, savings, etc) the check # field above (the field next to "No.") can be used very effectively if you develop and use a concise list of codes for the different types of transactions that you have.
Here is the list of codes that I use for my own books and all my clients' books:
(the actual check # used) = check
DC = debit card purchase
EFT = electronic funds transfer (items that come out of your bank account either electronically, automatically, or both). Examples of this would be electronic payments of payroll taxes, bank fees, automatic telephone or utility payments, etc.
BP = bill payments made with online banking
TX = a transfer between bank accounts if the receiving bank account is not a bank account that is tracked in your QB file. To record a transfer between bank accounts in the same QB file us the Transfer Funds function located under the banking menu. An example of when you would use the TX code would be when the owner of a sole-prop or a shareholder of an S-Corp transferred funds from the company bank account to their personal account. The actual transation what a transfer of funds online or via the phone. Use of the code "TX" will help track that.
WD = a withdrawal from the bank account. Use this code when in-branch withdrawals are made or the bank makes an adjustment to your account.
ATM = an ATM withdrawal from the bank account. Use this code when monies are withdrawn from the account via the ATM machine.
ADJ = an adjustment that you make to your bank balance. This code should not be used very often, if at all!
The codes above ARE case-sensitive in that you need to be consistent. Either use all caps (DC) or all lower case (dc) on ALL the entries. Don't mix using upper and lower case. Doing so will cause QB to sort your entries incorrectly in the Reconcile window.
Using consistent codes will help you in reconciling in that QB will group all the like codes together in the Reconcile window by ascending date (although in the newer versions of QB, you can change the sort order of the entries in the Reconcile window). Reconciling your account will be much easier when you can easily find the transactions in your reconcile window to match to your bank statement.
The list above are the codes that I have found thru my 17+ years of experience to be the easiest to both use and remember. Feel free to leave comments with any codes that you find useful.