My favorite type of crochet lately has been lace. I love making the intricate designs and using the fine cord. I don't go all out and use thread and a thin-beyond-thin hook, but I do sometimes use a 2.25 mm hook and thin cord. It's really fun.
The top two pictures are of a lace curtain I'm making for our upstairs bathroom. It's a half-curtain; it will cover the top half of the window. I ran out of thread/cord, though, so that project is postponed until I get to the store. :)
The two bottom pictures are of a doily I made out of red cord. I found the pattern recently in one of my magazines that I get every month, and I loved how it turned out!
For both projects I used a 3.75 mm hook and smooth cord.