Most people probably know about this, but in case you don't...
Google Docs is a free online service that lets you create spreadsheets. It's not as full-featured as Excel, but it's a lot cheaper and works very well for gear list purposes. Perhaps the most useful features for BPLers are:
1) You can authorize people to make comments and changes to the spreadsheet, so community help can be much more organized.
2) Everything is completely online, so you don't have to upload a file. Just put a link to the file in your post, and there it is for everyone to see.