I recently bought a new "brush tip marker" earlier this week. The trick about this tool, is that the brush tip is actually made of a hair like material, similar to a traditional paint brush. This allows you to make really dynamic linework, although it really took me some practice getting used to. But I am already quite smitten. This one is made by POSCA.
I am going to try out the Pentel Pocket Brush in the near future. This is a bit more expensive, but is also refillable (unlike the POSCA I've got). So it wil certainly be cheaper for heavy users in the long run. Also the Pental is favoured by many pros as far as my research go.
Below is a sketch that I just did using it. It was my first try, but I'm quite satisfied.
Take care! :-)