What's the best way to deal with a database with a big table with information that will RARELY be used?
You basically have a couple of options, but in the end if you have records, they must occupy space.

You can try to compress the data. This will reduce disk space, but has side effects (it can make queries slower, for example). And it may not be available in your version of SQL. If I remember correctly, in SQL 2008 r2, compression requires Enterprise Edition. Brent Ozar's website talks a bit about some other side effects.

Otherwise, the best you can do is either move the data to cheaper (slower) disks via partitions and/or file groups or work out a retention policy that lets you purge data past a certain age (possibly after exporting it?)