I always prefix the tags (and usually branches too) with the date in YYYYMMDD format, followed by a description of the purpose of the tag or branch.
e.g., 20090326_Release_v6.5 or 20090326_Post_Production_Update
This is under the standard trunk/tags/branches hierarchy of course.
The date prefix ensures that they all the tags or branches are displayed in creation order, which is much more useful then just being sorted by description if your scanning through a big folder of tags. You see the timeline of when and why they were created (like mini log messages).