First place is in the resources section of this guild where people post images or links to them. Personally I use circles and squares and label the name and then have a whole map for the place but some like to have mini pictorial views of the city to use. Have a look at Djekspeks work who does it by hand / wacom pen. Theres a few people who make icons and stuff to use. Check the usage rights. Most of it is CC licensed in some way - others is just use as you see fit and some more is non commercial but otherwise don't care. Ultimately tho I suspect that at some point you will have to get the ole pen out or try google sketchup which I am reliably told is very easy to use.