There are an increasing number of 'web services' available with which to add content to your maps. It is important to note that these services are only providing data for viewing, not for processing. That is, while you can display the data on a map, you cannot extract elements from the maps and process them (e.g., create buffers around features). (As stated on the BC Government web site: "This service does not contain any functionality to extract vector based features from the BC Geographic Warehouse."

ESRI's free services are described here, and are available through this URL: http://services.arcgisonline.com/arcgis/services. Instructions on how to connect to the ArcGIS services provided through that URL are provided here, and instructions on how to connect to WMS and IMS services (as described below) are provided here.

The BC Government has a list of available services here: http://www.data.gov.bc.ca/dbc/geo/wms/index.page. Instructions on how to connect are provided here. Note that most maps are associated with the BC Albers PBCS. (I found the easiest way to obtain the correct URL for the WMS is to right-mouse click on the WMS icon for the layer you are interested in and then selecting Copy Link Location. You can then paste the link into the URL window after clicking on Add WMS Server in ArcCatalog.)

If you do a Google Search for Web Map Services (WMS) you will find many other agencies are also providing data, such as Canada's DFO and the Atlas of Canada. The USGS also provides an array of useful map services here. (Click on the 'web site explaining the data' link in order to get the URL you will need to connect to the map service.)