Physical Basemaps

Finding free quality physical geography basemaps is a challenge. Most of the ones you'll find online will charge a fee to download. 

One avenue is National Geographic's Map Maker: http://education.nationalgeographic.com/education/mapping/interactive-map/?ar_a=1 
It has different map layers and a few have no labels (so your symbology does not interfere with text). Get your area of interest centered in the view window (away from the navigation icons) and take a screen shot. You can then import the screen shot into Illustrator as a static raster layer. You will not be able to edit the basemap (other than cropping/resizing), but it may be just the thing you want underneath your nifty map data. I'm particularly fond of the "terrain" layer which is text free and has nice hill shading. 

Another excellent source is Natural Earth Data. It is a site supported by NACIS (the North American Cartographic Information Society). It offers a variety of quality basemaps at different scales ready for use in ArcMap. Definitely worth checking out!

If you find another site that has good text-free basemaps for free (be it through downloads or screen shots), post a comment with a link!