The normal size of a business card is typically 3.5 x 2 inches.  However there is not really a standard when it comes to custom business cards – the size that you use really depends upon what your personal preferences are and if you want the cards to be compatible with any existing accessories that you may already have.
If you want something to be unique, then our designers at Printingblue.ca can work with you to create a business card design that is very unique to you.
While regular business cards are rectangular, you can also consider other options including die-cut (e.g. round corners, or a unique shape), tent fold business cards (business cards that open with more information inside), and magnetic business cards.