I've used one of the Chessex battlemats, it works fine. If you want to have really awesome looking encounter mats, try perusing the Dundjinni forums. Dundjinni's a mapping program. I've not bought it (I'm cheap!), but there's a bunch of talented and prolific people over there who've made some beautiful maps. You can print them out, slice off the margin and lay them out to make a very nice map. If you want to use them more than once, glue them to some kind of stiff backing like foamcore, matboard, or thin cardboard like in cereal boxes. I also recommend printing the maps on cardstock (a heavy kind of paper), it holds ink better and will lay just a bit flatter than regular paper.
rpgmapshare.com is another good source of encounter maps.
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Here's a map of "The Crooked Inn" that can stand in for just about any quirky/old inn
Here's a detail shot
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I've started using the 3D terrain and battlemats from
WorldWorks Games. Instead of buying a bunch of individual pieces, instead, for around $17, you get a themed pack of .pdf's for printing out as many terrain pieces as you'd like on cardstock. They take some time to print, cut, fold, and glue, but once made, they're surprisingly durable and can easily be swapped around and re-used to make all sorts of encounters. If all you're using the maps for is dungeon crawls, they've got a set that's real easy to make (if you can cut straight lines using a ruler and an x-acto knife) called DungeonLinx 2.5D. I've posted a pic of that below, along w/some of their other things. One pic shows all the pieces you can build using just their Castleworks Ultimate set. I've used its buildings to do up big street battle encounters, etc.
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