Don't worry--it will come! This is one of the many miles stones where there is a broad range of time what is "normal." My friends daughter who is 2 1/2 months younger than my son was walking before him. She started around 10 months and my son was about 14 months before he starting taking more than a couple of steps unassisted. With her already cruising and taking a couple of steps, she'll be on the move before you know it!
Here's an excerpt from Babycenter.com on walking:
Most children take their first steps between 11 and 14 months, but the normal range for reaching this milestone is very broad. Some kids walk as early as 8 months, others as late as 17 months. Don't worry if your child is one of the later ones — what's important is the progression of skills. If your child was a little late learning to roll over and crawl, chances are he'll need a few extra weeks or months for walking as well. As long as he keeps learning new things, you don't have to be too concerned.