Pop into your local comic book store, and there will be a selection of free ones from which you can take one away with you. This is an annual event on the first Saturday in May!
Not sure which books are in the offer, as I haven't been out to have a look yet! Will update later :-)
You can check to see if your local comic book store is participating by using this store finder - this does include *some* Forbidden Planets, but possibly not all. Use the checker below to make sure which shop in your town is participating, cos it could be one of the smaller retailers :-)http://www.freecomicbookday.com/fcbd_global.asp
Not sure if this is across the board but in my local in Hull they had Superman, Avengers, Aliens, TMNT, Sonic, X-Men, Hellboy, and a couple of others that didn't really stand out enough for me to remember! I could also pick up 2! Not bad for a freebie! These are current issues as well!