When software (browsers, Web servers...) supports elliptic curves at all, you can more or less expect support for the two curves given in NSA suite B, i.e. the P-256 and P-384 curves which are specified in FIPS 186-3. These are the same curves as the "secp256r1" and "secp384r1" which you list. The 15 standard NIST curves (from FIPS 186-3) are actually a subset of the curves specified by Certicom in SEC 2.
Some software implementations go further and support other curves. For instance, OpenSSL supports all 15 NIST curves (code was contributed by Sun and is believed not to infringe on any patent -- which explains why OpenSSL does not implement acceleration of Koblitz curves through the Frobenius endomorphism). But if you want to maximize interoperability with existing browsers and servers, stick to P-256 and P-384 (I think these are the only two which will work with Internet Explorer, for instance).