Total Network Inventory: Professional PC audit and network inventory management software - fits best for a for companies of all sizes. Free for 60 days.
Network Inventory Advisor - Network Inventory Advisor audits all network software and hardware simply and efficiently
Cisco Data Center Network Manager - Cisco Data Center Network Manager offers network management system (NMS) support for traditional or multiple-tenant LAN and SAN fabrics.
Lansweeper - Lansweeper discovers Windows, Linux and Mac machines in your network.
Silver Peak - Silver Peak's WAN optimization and replication acceleration solutions accelerate data mobility over distance for optimal application performance.
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
IT Manager - Monitor your networks and servers from one place