The trick with blog commenting is that you want to get a nice high quality comment on a blog that has high volume traffic.
Many people stuggle with this, but It is not as hard as you think.
1) Just go over and use google alerts Google Alerts - Monitor the Web for interesting new content
2) in the search box provided, type in your search keyword without hitting enter.
3) the results will show up automatically
4) Then, in result type: select blogs
5) Then, in how many : select only the best
This will narrow down the field to the best blogs that have the best content and higher traffic.
You can change the other search parameters to find more blogs if you want.
But this is a great way to find good blogs with good amounts of traffic to post a high valued comment on.