Charge money for advertising in it.
Charge money for advertising in it.
Keep the PDFs free to download.
Have a Member's Support Brigade (stolen concept from thesurvivalpodcast.com) which includes free e-books from other people and coupons for other people's products.
Charge for print copies.
Sell a subsciption which gives you a special Ipad version or whatever.
Put in ads.
Sell a "best of" volume via Lulu.com.
Make our own spin-off e-books and sell.
Merchandise (t-shirts, stickers, etc).
Amazon store (books we recommend, stuff like that).
Use kickstarter.com to raise money for specific sub-projects (like "start a hackerspace").
Any more ideas?
Alternatively just copy the Hacker Monthly business model, apply it to your content. It seems to work and it would be easy to copy.