I don't know of any free website that will do this for you. I'm cheap so I do it myself.

You can put your own grid lines on there. This is easier than it sounds.

I assume you're working in lat/long and not military grid reference system (MGRS).

You will need a color printer, a ruler and good black pen.

1. Go to www.topozone.com. Click on 'View Maps'. Use the Place/Name search to find your area.A typicalLat/Long for my area is -Latitude: 36 degrees 14 minutes 56.1 secondsLongitude: 76 degrees 08 minutes 47.3 seconds. Your GPS will go down to the first decimal place in this selected format and this is sufficient accuracy for very precise stand placement (+/- 20 feet). Numbers changed to protect good spots!

2. When the map comes up select the following settings:
1:24K/25K Series
Map size: Large
View scale: 1/50,000
Coordiante format: D/M/S
Un-Check 'Show target'

3. Use 'File' 'Print' to Print out sections of the map you need. Note: You may have to print1-3 pages and carefully trim/cut/glue to get the exact are coverage you want.

4. Go back to place name search and scroll down to the section titled 'Latitude/Longitude - Degrees/Minutes/Seconds'. You will need to input a series of points that represent the corners of the squares in your grid system. Map settings are not critical at this step, but you will need to click 'Show Target' so that the map will depict the exact placement of the corners.

5. To do this, you will round lat/longs to the nearest 10seconds. Example: Latitude: 36 degrees 14 minutes 50.0 seconds Longitude: 76 degrees 08 minutes 40.0 seconds would be the corner to the south and east of my example lat/long from step 1. Transfer each of the corner points to your printed map.

6. After you have inputted all of the points, simply go back and connect the corner dotswith your ruler and black pen.If you use settings from my example, youshouldget 1" squares which is about the same as the military maps. If your squares are smaller or bigger, don't sweat it. You can play with different scale settings in step 2 if it bugs you. Laminate the map for waterproofing, if desired. You can also label the grid lines on the edge of the map, if desired (40.0, 50.0 etc).

Post back if you have trouble.