Depends whether you're looking for a stand-alone Network Management system or are looking to integrate it with something else. The Tivoli solution is great if you're wanting to integrate with TEC then there are few solutions to match it.
You mentioned HP OpenView - comes from the same stable but my experience is that it's difficult to install (it's been a while so maybe it has changed).
I'm currently working with Aprisma's SPECTRUM product and I'm pretty impressed with it.
BMC have released an Enterprise Management product. I've no experience of it, but if you're looking to install Agents and manage servers etc in future this would be one to look at too.
Lots of point solutions and freeware/shareware so if you have a limited budget, you can usually cobble together a number of these products to do what you need.
My personal favourite in all this is NetView, though again, each have their own strengths and weaknesses.