I do not work for the company that makes the product I am recommending, nor do I have any affiliation, relationship, association or any other connection to them except the one where I give them some money every year and they let me use their product in return.
I use and recommend a product called Lansweeper. The cost is very reasonable, uses WMI, and SNMP for asset scanning. It can do everything it's designed to do without an agent or you can deploy a small, non-resident agent if bandwidth considerations are critical. It stores all it's information in a standardized SQL format (can use MS free SQL express) if you don't already own SQL in your environment. It's reporting capabilities are fantastic. The interface is all web enabled and can run on it's proprietary web hosting or can use IIS.
We pay $1500 US once a year and the license allows us to run as many scanning servers as we need. There are no limits on the number of nodes that can be scanned or data that can be stored. Maint is so easy you can have a low level tech manage the thing. And because of the standardized data structure, several of our other organizations pull data from it daily. Our ticketing system (Service Now) has regular reporting and direct ties into the lansweeper database. Security is not the primary focus because it is meant to be entirely internal with no public interface. however you can limit access in a very granular way using AD security groups or individual ID. It scans MAC, Linux, switches, routers, cisco gear, VOIP, windows workstations and servers, you name it. It also has a fairly robust software management component although we don't rely on that set of features as much as we could.
We've been running it in my company for over three years now and even though we have SCCM, Service Now, Sailpoint and a number of other products that are critical for very niche requirements, everyone in the IT organization that has need to gather and maintain asset management uses this product and I do overhear them talk about it with respect, especially when you consider the cost. Not going to link to their site but you can easily google Lansweeper to get there. The company is out of Belgium I believe and I found them by asking questions in the BSA forums.