I tried all the stuff I learned to increase link popularity -- web directories, link exchange, article directories, blogs... Are there anything more besides these? Also, will too many articles, link reciprocals, and exchanges hurt PR?

Lots of content ... lots of unique articles ... lots of unique content on your site that people will want to NATURALLY link to - viral marketing at its best.

Wait.
I'm new to the term... How does it work?

Viral marketing ... basically when you invest a little bit of money in a big idea that catches on, and it just spreads and spreads, like a virus. An example is creating something so catchy that word of mouth just spreads like crazy about it, and you have to invest few advertising dollars into making it very popular.

Many sites have tens of thousands of articles/tutorials/etc. So no, I don't think you can overdo that. Every page is a potential landing page for a visitor who was searching on Google.

There are lots of other things you can do for your site. Do like Dani, and get rid of query strings. Google likes plain .html files. While Google will index a page like "index.jsp?id=553cd5566" in my experience, such pages are given lower rank if they're indexed at all. You can use mod_rewrite to do it. Search for it on Google.

Reciprocal links don't really hurt or help much anymore. At least, they don't help with PageRank. They probably help send a few human visitors to your site, though. And that's good. But Google seems to have decided that if the link is reciprocal, then it sorta balances out. One-way links are much more powerful.

Also, you've not mentioned SEO. If you haven't looked into that, then you need to do so. It basically involves re-factoring your pages to be more search-engine friendly.

There are of course many more ways to promote a site. Obviously, you can and should take it offline. Give away bumper stickers, t-shirts, mugs, anything with your URL on it. Run print ads. Do radio interviews. Issue press releases. Those things don't have much to do with PageRank, other than reducing your dependency upon it.

-Tony