Best method I've found is to recreate old and expired web sites that once had good pagerank. There's still a truckload of old and expired domains out there that have lots of links that nobody knows about.
In this forum I won't reveal how to find them, but assuming you come up with your own system, you then go to the Wayback Machine and recreate the old web site from scratch by copying the code from the archives. This time you add a few of your links and pass on the link juice.
I admit it ain't easy, it can take a day or so to find an old expired domain with lots of PR4 to PR6 links to it, but trust me, it is worth the time and effort.
I have bought PR4 and PR5 domain names for as little as $15