Downcast (iPad / iPhone / Mac)
A powerful wee podcast app.

Marked 2 (Mac)
A previewer for Markdown files.

Pinboard (Web)
A bookmarking service, sorta like Delicious was way back when. You click a bookmarklet, fill in as much or as little info as you want about the page (tags / privacy etc) and it's saved to your account for accessing anywhere.

TextExpander (iPad / iPhone / Mac)
Changes short pieces of text into long pieces of text.

Tweetbot (iPad / iPhone / Mac)
My favourite Twitter client. Works particularly well if you use lists, I've found. Follow me on Twitter: @davidgalletly