D

What does /prog/ think of it? I've been using C++ for the last three years and some of D's features sound cool, so I might consider switching.
What's D's performance in relation to C++?
Does it standard library not suck? (In particular, I'm interested in structures such as strings, vectors, lists, queues, etc.)
Are there good IDEs available?

>>1
There are two "standard" libraries - the official one, Phobos, which is quite good but has no containers, and unofficial, Tango, which has almost everything, but some say it is too much modeled after Java's standard library (classes everywhere, etc.)

Just use Tango and give it a try. Compared to C++ the experience should be quite enjoyable.

>>2
Code::Blocks is usable. It doesn't support all the syntax (for example, /+ +/ nested comments) and sometimes understands the code as if it was written in C++, but generally makes programming in D easy. Also, it cooperates with GDC/DMD compilers out of the box.

Compatibility with C is harder because of two things - many libraries (ab)using the preprocessor in their header files, and D using Pascal-style strings instead of C-style.

Overall, I see a bright future before D - C++ will become more and more confusing, and D is almost as fast, simpler, and more powerful.

What can be dangerous to D is the author himself - Walter Bright shows some benevolent dictator for life-like tendencies, like that time when he was arguing that opEquals should return int, not bool, and it took a few years to convince him and change it.