The games mentioned above are wonderful. I have after-school classes two nights per week that last nearly two hours. I usually start with a fun icebreaker game (Two truths/One lie, "I Have Never...", the "survival" games, etc.). Then I'll teach them a bit, like an English expression or two for the day that they write in their notebook and we practice. To wrap it up, I alternate between showing video clips with worksheets and/or playing more games (Uno, Jenga, Clue, etc.). As mariag said, keeping it lighthearted is best. At first, I put in a lot of effort and tried doing serious stuff. It failed miserably.
Another alternative that has worked well for me is to follow a theme--you can easily find plenty of material under the "Summer/Winter Camps" section. I used the "Detective Winter Camp" for my night class last semester, and they loved it! Now that I keep it fun, both I and the students enjoy class more!