You may not think of a saddle cover as being a necessary item for your bike, but if you ride daily and year round, it's a guarantee (especially if you live in Chicago) that your saddle will be affected by precipitation, or even excessive sun. Some saddles can be damaged by rain and other moisture. In other cases, it can just be uncomfortable (or a faux pas) to ride on a wet saddle, thus soiling your clothes. Since we have to deal with these obstacles regularly, we tried out a number of the waterproof saddle covers on the market and found that the Jandd version was one that's truly waterproof. It comes in two different sizes. If you have a saddle that's more of a road-style saddle and not particularly wide, we recommend getting the medium.
If you happen to have a Brooks leather saddle, owning a saddle cover has the ancillary benefit of camouflaging your eye-catching saddle from would-be thieves.