There are many websites and blogs dedicated to all sorts of information about Revit, from tutorials to downloadable content, though there is very little that is specifically for site/ landscape design.
In addition to my Revit Posts, Revit Families, and Revit Landscape Training Course, here are a few more resources that might be helpful.
Components/ Families
RevitCity. One of the largest sharing sites, and thus has a large selection. Quality of content can vary widely. Free. Requires login.
Bega. The US website has Revit families of most BEGA lighting products (of those available in North America). Click on product number, “Revit BIM Model” will be listed under Technical Information. Free. Does not require login.
Landscapeforms. All exterior furniture products available as Revit 2015 families, though all geometry is import dwg. Free. Requires email registration.
Autodesk Seek. Very limited, though a few site product manufacturers: SiteScapes has site furniture, greenscreen has green wall and screen families, and decent selection of street and roadway lighting. Free. Requires login.
Landscape BIM Blogs (by Revit users)
Landscape BIM. by Henry-Fenby Taylor, landscape architect in the UK
Revit Landscape. by Åge Langedrag, architect/ BIM Innovator in Norway
Online Communities/ Forums
Not all are landscape-specific, but are still good resources for general Revit questions.
landarchBIM 
The National BIM Library in the UK is slowly being populated with landscape resources. There are several paving and walling types there now:
http://www.nationalbimlibrary.com/Search?searchTerm=landscape
Hmm. Hopefully the quality of the content will start to improve. Just checked several of the walls and floors, and I can easily make better stuff in 5 minutes. It’s almost pathetic. But good to know anyways. Thanks Chris.
Yeah, the content is more beneficial if you’re in the UK and actually using those paving products – they come with a whole host of parameters completed that will write out correctly to IFC and COBie. If you’re just looking for free hatch patterns or textures etc, they are certainly less useful…
Holy project parameters. Surely those aren’t all necessary? That would be reason enough not to use them. While it is good that they have correct IFC and COBie data, it would be better if they looked half decent as well.
We do struggle with the number of parameters that NBL use, but I think the industry will have to get used to that. We use lots of NBL families within our building models (doors, windows cubicles/stalls etc). The good thing is that NBL have just published a national standard for BIM content in the UK, which has a good section on ‘parameter hierarchy’ which means we can now nominate the highest ranking parameter for a particular property (e.g. Fire Rating might have a system parameter, a COBIe parameter, an NBL parameter etc) and map all the other functionally-identical parameters to that one. This stuff is essential if you have to issue COBie.
http://www.nationalbimlibrary.com/nbs-bim-object-standard