Warning: not an engineer, please read comment accordingly.
I have to agree on the Sakura. I've used a Micron, and the non-technical Gelly Roll, and they've both been wonderful: the ink has been smooth, with never a blob, smear, or dry spot, and the pen itself writes quite smoothly.
I'll also put in a recommendation for the Zebra Sarasa Clip. I use the 0.4 mm tip, and it can feel a little bit scratchy, but I naturally write quite small, so the precision of the fine tip works well for me. The ink is very consistent, with no blobbing whatsoever. Once in a great while I do hit a dry spot, though. It's also light and comfortable in my hand.
I don't know that you can actually get that model of Zebra here in the States, but I use JetPens. They have a good selection of different writing tools (mostly from Japan), and they're very speedy: I've yet to place an order using regular mail that has taken more than 3 business days to get to me.
...ugh, now I feel like a salesman. Which is slightly mitigated by the fact that I'm being a pen salesman.