Here we first meet Penny. She is originally shown to be a stereotypical "dumb blonde" compared to the highly intelligent Leonard and Sheldon. However as the show progresses we see how Penny, in fact, is smart, witty and confident. In some episodes in season 1 Penny has a side fringe and long choppy layers. In others she has a full front fringe and shorter shoulder length hair. When she has a fuller fringe she looks a lot "cuter", personally I prefer the hair she has in later seasons.
Season 2 / 3
Season 4 /5
Other Penny Styles
Penny also wears a her hair in a variety of different styles throughout all the seasons. For example a high ponytail when she works at the cheesecake factory and a messy bun when she is lounging around in her apartment. She also wears a lot of cute half-up styles.
The best way to copy "The Penny" is to 'poof' up the front of your hair or back comb to create volume at the crown. Styles are usually left messy and informal.