the trek/bontrager and specialized butt-o-meters are a good starting point and will get you on the right width of saddle most of the time. if you're right between sizes it will be no help, but otherwise you have at least taken care of one of the variables mr. ratliff pointed out.

finding the right width, though, unfortunately is only a tiny portion of the search.

1. find a good local shop with at least 30 day exchanges and a good inventory of saddles to try.

2. bring your bike with you to the shop if possible.

3. have an infinitely adjustable seat post. a basic seatpost with notches is often inadequate to set the best angle because the rate of change is way too high. you can't make a small tweak, and often a very small tweak is exactly what you need. there are many seatposts that loosen and you set the angle where you want. thomson seatposts have two bolts that pull against each other and a degree marking, which makes it the easiest to use when switching saddles.

4. consider using a level to make small adjustments. it is hard to eyeball changes, especially if you don't have a thomson seatpost, and a small level helps a lot. you won't be able to level different saddle shapes, especially those that kick up in the back, but the bubble doesn't need to be centered. just watch the effect of changes you make.

5. if you don't have good saddle fitness already, every saddle will feel uncomfortable. this one is important for new riders.

6. wear cycling shorts when demoing saddles if you ride with cycling shorts. (and you should be.)