A quite a lot of software have 64 Bit support now, not just Avast and Vistual Dub.
Here is a site with completely dedicated to 64 bit computing right from Softwares, drivers etc.
Should help you ,
http://www.start64.com/
64 Bit does not necessarily give you a Speed advantage, You need an OS and the Softwares to use the 64bit advantage which unfortunately is not huge enough to be noticed today.
Quoting Wikipedia -
While 64-bit architectures indisputably make working with huge data sets in applications such as digital video, scientific computing, and large databases easier, there has been considerable debate as to whether they or their 32-bit compatibility modes will be faster than comparably-priced 32-bit systems for other tasks. In x86-64 architecture (AMD64 and EM64T, IA-32e), the majority of the 32-bit operating systems and applications are able to run smoothly on the 64-bit hardware.