Yeah, it's a tough call. I can see R being very useful, but ChucK is way more fun. C just seems like a book that needs to be written before the "learning C sucks" situation gets worse.
There are usually a ton of acceptable beginner's books and then very specialized and complex books but very few good "intermediate" books like the favorites:
- TCP/IP ilustrated - Perl Camel book - R&K C book - Silman's groundbreaking chess books - Harrington's groundbreaking poker books