FeedCatch is a nice little tool that allows you to take any feed and archive posts indefinetely (or less so if you set the parameters to do so). there are a number of default options, including:
It takes just a few seconds to set up a feed and choose the parameters for archiving. Headlines and some summary text are shown.
Note that you can use the FeedShake service to create a merged/sorted/filtered feed from multiple feeds, and then archive everything using FeedCatch.
Check it out. The service is free and requires no registration. The TechCrunch feed we created is here.
There is a bug report that is being worked on. Hopefully this will become stable (and therefore useful) sometime soon:
2005/08/06 08:30 GMT :: All items stored before this date are deleted to fix a bug. This may happen again so do not expect FeedCatch to store any stable data this week. Link