Labeling Food for the Freezer
As mentioned in comments, masking tape is an excellent solution. It's cheap, it holds well yet comes off easily, it can be torn off at whatever length you need, and you can write on it with just about anything.

Both at home and working at restaurants, I've used masking tape and permanent marker for labeling items for storage in the pantry, fridge, and freezer for years. Just about its only disadvantage is that it's not aesthetically pleasing, but presumably you're not usually showing off your collection of frozen meals. It can also sometimes leave behind traces of adhesive after being stored for a long time, but that's easily scrubbed off by hand.

A couple extra tips:


The regular beige stuff is fine; there are blue "painting tape" varieties that claim better adhesion and easier removal, but they're not worth the extra money. Plus, if you're writing in black marker, beige offers better contrast.
Labeling is easier if you tear a strip off the roll before you write on it. I don't usually have problems with the marker bleeding through, but you probably want to write on a non-decorative surface in case of stray marks.
Where possible, stick your labels on lids (if you'll be reheating in the same container) and pull them off at room temperature. Excessive heat or cold seems to increase the chance of residual adhesive, and you probably don't want even a mild, temporary glue cooking in your oven or microwave.