Here's a fun one that'll still fit into the remainder of your summer: the hundred pushups challenge. Start by assessing your pushup ability (or not) and then proceed accordingly through the six-week program. I'm doing week one right now and loving it... and also doing the two hundred squats challenge, which is proving very (i.e., painfully) effective.
And for while you're working out: download some free audiobooks at Books Should Be Free. They have G. K. Chesterton, Jane Austen, Sir Arthur Conan Doyle... tons of great classics. And lots of George Macdonald, too, so of course I'm happy.
Two weeks until Conventiculum. Woohoo!