Yoga can be hit or miss as an athlete. If you don't know what to expect, you may end up injuring yourself rather than benefiting your training. While I like going to a studio to practice with a certified yoga instructor, often there is just no time between running, lifting, kids, work, etc!
There are a number of amazing online resources - both free and paid.
For runners and athletes looking to gain the benefits of yoga, like stretching after a run or building core strength, you can see the benefits by doing small daily or every other day practices. Even 10 - 15 minutes daily can make a big difference.
For me personally, I have instituted a 15-minute practice after my run. I come home and have a mat set up in my garage (so on weekends when my kids are not at school, I don't go back into mom mode right away). Often I do my own thing based on my years of practicing yoga, but occasionally I turn to an online resource. Below are the exact videos that I recommend and what purpose they serve.
If you want to level up - and invest in yoga as a part of your training, begin to learn more than the poses, there are two great online resources that I have used - JasYoga and YogaGlo. They serve slightly different purposes though.
For free yoga classes, there are a few that I like through youtube.
For someone who used to practice at a studio but just can't make it now and looking for a more involved practice to do 2 or 3 times a week as cross training: