favorite pen for writing kanji?

I'm finding that writing the characters is helping me remember them. None of the standard ball point pens I've tried 'feel right' for writing kanji. Aside from fancy calligraphy sets, what style/brand/model/size of pen do you like to use?

I just tried out a bunch of different pens at the bookstore on campus and found one that feels better than the rest, but still isn't quite right. It is a Pilot G2 05 Ultra Fine Point, in case anyone is curious.
I like using a fudepen (hard tip style), or failing that, a mechanical pencil with 2B lead (anything harder makes writing smoothly harder imo).
HB wooden pencil, well-sharpened.
I remember things not feeling right when I started learning the kanji. I also tried to use nice pens instead of any old, scratchy ballpen. But, I think it might actually be more of a case of just not being used to writing in Japanese. The muscles in your hand/arm are having to learn to move in different ways too.
Since I finished RTK and started doing sentences (AJATT method) my handwriting has become better. I'm still using the same type of pen as before, but writing several pages of Japanese a day is obviously having some effect. It is most noticeable in my hiragana as those are written more frequently, but the kanji are also 'flowing' a bit better now.
I like the Pilot VBall Grip (0.5mm). It has a rubber grip and marks are small. I was using a hexagon shaped pen with a ball point, and the biggest problem was that the shape of it gave my finger a callous from writing all those kanji. I agree though that writing kanji out is a great reinforcer. I incorporated it in to each review step:

1. I have a notebook for writing down each Kanji and a story if I can come up with one as I go along from the book.

2. During the review, I test if I remember it or not by trying to write it in a separate book.

3. During the failed study, I do the same.

I think Heisig said not to do this, but it works for me.

If you're going to write a lot, make sure you have a rubber grip! The callous doesn't want to leave anytime soon!
Edited: 2007-11-09, 9:00 pm
When I'm just practicing kanji, I like to use a little whiteboard and fine tip dry-erase marker. It feels a little brush-like, and because you don't have to press it won't fatigue your hand as easily as pen on paper.
Edited: 2007-11-09, 11:08 pm
My pen of choice (for kanji and other purposes alike) is the BiC VelocityGel 0.7mm. I love the "feel" of writing with gel ink, and this pen actually keeps working until it's completely empty, as opposed to drying up while still half full like some other models I've tried. It also has a rubber grip that I find very comfortable.
I also use the Pilot G-2 .05 ultrafine. I like the way it can write very small and yet still make the tapering off strokes and hooks. I do a lot of writing and have tried a lot of other pens. Other fine points and calligraphy pens I have tried are either uncomfortable to write with or don't have the smooth liquid flow of a gel.
I use Pilot pens also, I have a Pilot G3 0.7, It's a nice writer, smooth flow, I'm looking to pick up a fude brush tip pen for special writing, but for everyday writing in Japanese i use my Pilot or a Uniball signo.

I never and don't suggest that you do use any pen that isn't gel ink, the pigment makeup of regular pens just doesn't flow well enough for Japanese writing.
I started out by using an HB-pencil, but soon moved to my good old fountain-pen. So far it's working ok for me; I prefer the blue ink to the light grey of the pencil.
I might go and buy some fancy pen when I'm a bit more advanced and want to really work on improving my handwriting or even start to dab in calligraphy.
I, too, like the Uniball Signo for just about everything. But like Biene, I've been into using a fountain pen since the summer and I've grown fond of Waterman's blue-black ink.
If you live in Japan, I recommend trying out a brush-pen. They are a little bigger than an average pen, but they have a small bristled tip that resembles a calligraphy brush. Don't forget that kanji are supposed to be written beautifully, and that the overall aesthetics are only the way that they are because they evolved from the tip of a 'fude'.
Why only if you live in Japan, Pentel make a good brush pen that is distributed worldwide, I got mine from:
The brush pens are actually pretty cool, but I found that I focus more on the looks of the kanji and it winds up being a shodo/shuji kind of thing which is not a bad thing at all. But for strictly trying to study, everything else writes smaller and faster which is good if you don't want to waste lots of paper or time.

I still like my fountain pen, but to be honest, I've been writing lots on the touch screen of my new gizmo. Smile
There are various kinds of fudepens, the ones with the firm tips tend to be shorter, and thus let you write the kanji quite small. In terms of character size the one I use is about the same as writing with a .7mm pen.

That Pentel Brush Pen looks to be means for writing larger characters and thus not particularly suited to normal kanji practice (you'll use way too much paper). If I'm wrong someone please correct me as it looks like an otherwise nice pen.
It's a fairly large writer, rougly the size of two lines on standard lined paper.
I'd recommend a nice fountain pen.
I've thought about fountain pens in the past, but couldn't justify spending a minimum of $25 on an entry level one to check out how they work for kanji. However I just did a search and discovered a disposable one that seems to go for about $2 on average. I'll have to keep an eye out in stores for it. Non disposable ones also seem like a pain with the mess of bladder refills, tip maintenance, ink drying up, etc.

Only real reason I'm entertaining the thought again is because I currently don't have a reliable supply of 筆ペン as I'm out of the country atm. When in Japan I just use disposable 99円 細字 firm type 筆ペン from 99shop or だいこく。You can make very nice looking kanji in a minimum of space with those. The 筆ペン linked earlier is a 中字 soft tip which is impractical for use with your srs drilling (use way too much paper) or for handwriting (ペン字) practice (soft type 筆ペン are supposed to be held differently). If you want to practice some 書道 though, they're great.
Edited: 2007-11-23, 4:00 am
for me ive tried loads of pens but the best one i love to write with is the standard hexagonal yellow bic fine. It just writes well. The other bics made of transparent plastic write thicker but i find are more stubborn and tire my hand out.

I did see a quick way to hack a g2 pen to use montblanc refills on Cheap way to get $250 ink rolling i suppose.
Just got myself a Pentel ERGoNoMiX pen, truly the most comfortable pen I've had thus far for writing Kanji, the Ink is almost the same as the great ink in my G2 & G23.
Have seen students with this. Really weirdly shaped. Might feel one up if I get the chance. Wink
It's a really good pen for kanji, the wrist rest does get a little annoying until you find a perfect setting for it to enhance your writing.