I'm not sure on what you want to focus the lesson. Do you want to teach the future tense "going to" and planned activities? "will" and spur-of-the-moment decisions? some combination of both? verbs related to weekend activities? prepositions of time? The possibilities are endless!
However, I can direct you to a great site for pictures which I use for all my curriculum needs. There are only photographs available, but they are professional quality... and they are free... and there are thousands to pick through! (You can look at my ESL website for a few examples, as well as how I place them in my handouts.)
The photograph site is stock.xchnge at: http://www.sxc.hu/index.phtml
My site is at: http://www.headsupenglish.com
Good luck with the lesson!