When it comes to alternatives to Windows' Task Manager, it's hard to go past Mark Russinovich's Process Explorer, but if you'd like to try a new utility -- especially one with a feature such tools usually don't come with -- then Listsp is worth checking out.
Listsp is an open-source tool that does the regular duties expected of a Task Manager replacement -- you can view active processes, running services and network activity, though the latter lists applications with port connections, rather than a graph of incoming / outgoing data. What separates it from similar tools is the ability to view active drivers also.
This information usually requires diving into the registry to discover, whereas with Listsp it's presented in a readable and functional format.
All in all, it's a handy program, though I do have some gripes. Refreshing can sometimes take a long time and performing sorts via clicking on column titles does not happen instantly, something Windows' Task Manager and Process Explorer handle without issue. Even when sorting does occur, items appear to be only sortable in ascending order, which isn't horrible but certainly inconvenient.
Listsp is not perfect, but the aforementioned interface issues can be ironed out in later versions. For now, if you're looking for a little more information from your process-monitoring apps, be sure to give this a download.