I believe I have some good suggestions to improve the C++ language. Who should I contact to discuss this? Do I have the chance to be heard, especially if I'm not a renowned expert?
According to this page on the C++ committee's official web site:
The public can submit proposed defect reports via the Internet news group comp.std.c++
You can access comp.std.c++ via groups.google.com, but it's better to get an account on an actual NNTP server (I use news.eternal-september.org, which is free of charge) and use a new client (Thunderbird does this; I use Gnus under Emacs myself).
I recommend browsing the group before posting, just to get a feel for how it works.
Note that revisions of the standard only come out every few years, and a new one was just published on 2011-09-11. I don't know what, if any, work has started on a new revision.
You have a 100% "chance to be heard," but you should be aware that the goals for the C and C++ language standards are quite conservative. There's billions of lines of C and C++ code out there and breaking changes are viewed with extreme reluctance. And, like any long-lived group, they probably are a little suspicious about new voices. As @Keith Thompson suggested, you should probably start with the NNTP groups, just to get a sense of the technical level of discussion.
Depending on how radical your changes are, the wisest thing to do might be to gather your changes and implement them under a new name and see if they gain any traction. Once they've been tested and their interaction with the broad world of C and C++ code is understood, you'd have a better chance of having them incorporated into the language.
(And note that the C committee doesn't have the same relationship with comp.std.c that the C++ committee has with comp.std.c++. But comp.std.c.is still a good place to get feedback on any proposals for the C standard -- as long as you're aware that there's nothing official about it.)