I've been using a 'Battery Tender Jr.' for about 3 or 4 winters now, to maintain 2 batteries for my vehicles in storage Dec - May. You can judge for yourself if their product is worth the money. They have a fairly good (slightly biased) electonics discussion on the subject too.
http://batterytender.com/default.php?osCsid=9ddbb1fd379cd753442343679314c19c
I think they are. I also have a gazmo that disconnects the battery when it discharges to a point below which the starter won't turn over, called a 'Priority Start'.
http://www.prioritystart.com/ Somewhat expensive, but peace of mind for cars that are used very infrequently (and which have a problem with slow discharge, another subject)