In addition of being a cartoon fan, I'm also an aspiring cartoonist. Lately, I've been experimenting with various tools to ink the strip. I'm particulary fond of Rapidograph, but the lines were too uniform for me, so I decided to set out and try brush...again.
Back in Japan, I bought a Kuretake brush pen. Several cartoonists (Norm Feuti and Brian Anderson in particular) uses it. It's very expensive to get the pen in US, going over $50 in some retailers. However, it's very cheap to get one in Japan; about 700 yen, which is roughly $5 in exchange rates.
The pen, at first, gave me frustrations. It was coming out too thick when I used it, despite all the practice. I eventually gave up and stopped using it...until now.
I took the pen with me to America and recently, I decided to try it out again, and what do you know, I liked how my drawing came out. I don't know if it's because my artwork improved or not, but I was very satisfied with it and am now devoting my life to it.
So if you like to use brush, here's a pen I'm recommending. Sure, it's expensive (unless you live in Japan), but in the long run, it's cheaper than sable brush, which you have to replace after it wears out. Kuretake's tip is nylon, so it doesn't wear out unless you're really rough with it.
Oh, and don't bother with the cartridges. Just get a jar of ink and dip it.