There's no one size fits all.
Cisco's enterprise class solution is CiscoWorks LMS: http://www.cisco.com/en/US/products/sw/cscowork/ps2425/index.html. It's a very full featured configuration and fault management tool. It's performance management capabiliites are lacking in areas most folks are looking for and many CiscoWorks shops often end up using a third party tool such as MRTG (open source) or Solarwinds for performance monitoring. LMS will set you back on the order of US$20,000.
A small Cisco-only shop may get by with Cisco Network Assistant, a rudimentary tool with limited device support. See the product data sheet for details: http://www.cisco.com/en/US/products/ps5931/index.html. The price is right - free
Solarwinds (http://www.solarwinds.net/) and Whats Up Professional (http://www.ipswitch.com/products/whatsup/professional/index.asp) are two good third party tols that many folks use happily. Solarwinds runs about $3-4,000 once you buy all the components and What's Up about $2-3,000.
