Just going to spitball this one, if you don't mind. Feel free to take or ignore any of this as you see fit.

• Sponsorship could go well, and if you're worried about low-quality sponsors simply decline anyone who doesn't met your set standards (it helps to have those standards outlined somewhere too).

• If you haven't yet, consider publishing a book with the best designs and possibly reach-out to the designers/teams to provide insights into their process/reasoning. That type of book could do well (just look to "Web Designers Idea Book" for an example of what's possible).

• Paid memberships could be an option too. I'd pay $5/mo if it meant I got insight news and interviews with the top developers/designers behind some of these apps. Even offering members something like the ability to vote on designs (exclusive to members only) and all of that could be worthwhile. $5 is chump change for many people in your market.

• Start outlining best practices as seen in this apps. Obviously you're looking at all of the shots that come in (right?) so you've got to start seeing a lot of unique trends, etc. You could easily collect insights you've seen and create an ebook/guide with those insights, sell it for $15 and you could easily recoup your $2k costs (you'd have to sell just 133 copies).

• Become an Amazon Affiliate. Depending on how much traffic the site gets (and whether you have an email list or dedicated RSS following), Affiliate links can build up revenue really fast. I just started implementing more affiliate links on my own blog and with 100,000 subscribers that's led to some months where my affiliate check covers my (very expensive) rent. You could easily sell design-oriented books and tools, etc. with your audience.

• If you have any spare time, consider making Pttrns into a consultancy. Again, if you're looking at and evaluating all of these designs, you likely have some valuable insights into how iOS designs can be done as well as how they should be done. Sell that as a service ($100/hr to start) and if it goes well after some time that could be your full-gig. Hell, I'd love to work with you to consult.

• Boost donation requests. Donations can work, if done right. The number one problem with donations (in my experience) is that most users don't realize it's an option (or that $5 really can go far). Stick a donation button everywhere you can, but do so intelligently and with clear indicators that "donations help this site going."

Good luck!