[inigyou]

One of the most conceptually simple ways to make a vacuum is a Sprengel pump. You have, from top to bottom, a pipe full of mercury, a restriction so it comes out in drops to the next stage, a chamber where the vacuum is developed, and an exit pipe. Mercury drops fall through the chamber, trapping air between them as they fall down the exit pipe. The energy comes from lifting the mercury back to the top.

A way that's easy to execute, but doesn't produce a perfect vacuum, is to fill a chamber with steam (actual high temperature steam, not the clouds coming off a kitchen pot), seal it and cool it. This is only a near-vacuum because it's filled with low pressure water vapor, but it's very easy to do.