Finding topographic maps online is not hard, but it can be difficult to print readable ones. Here are three sites to try:
Digital-Topo-Maps.com - This website uses Google Maps to pinpoint your US or Canadian location. Zoom in as much as you like, then click "MyTopo" to see the topographic view. Scroll down for the printing option (landscape or portrait). You can also purchase topo maps by using the links on the right. Scale may vary, or you may have to print several sheets in order to get the detail you want.
MSRMaps - This site is called Microsoft Research Maps and seems to be powered by Microsoft's search engine, Bing. Finding a US location is easy - just type in the address (as much or as little as you want) or latitude and longitude. You can also click the tiny map on the left to zoom in. Adjust the map size with the little boxes on the top left of the viewing area. You can see an aerial view or a topo view (or in some cases other options such as Urban Areas). You're allowed to download, email, or print maps. If you choose to print, it'll open a new window and give you options for resizing and changing paper size.
You can also click "Famous Places" at the top right of the screen and get a list of all kinds of places from sports stadiums to airports to landmarks such as Alcatraz or the Pentagon. Even if you're not looking for anything in particular, it's a neat site to browse.
USGS Store - On the right side of the screen is a link to "Download" Topo Maps Free. (If you click the link for "Topo Maps" you'll get an explanation of the different kinds of maps available.) Follow the instructions for finding a US location and for downloading. (I'm not finding this site easy to use. I don't know if it's because I'm using Firefox or because I'm just not patient enough to play with it, but I suggest trying one of the other sites mentioned here first. However, if you want to place an order to purchase a map, this is a good site.)
The US Geological Survey also has maps for sale and you might be able to see some really cool maps on their website, but printing may not be available.
If you're outside the US or you need a map for another country, do a Google search on your location of interest and add "topographic map." Most countries should have some kind of geographical department with maps available. You might not be able to print one for free, but you can probably purchase what you need.