Insoles are sooo IN right now.

As a shoe salesman on commission in 2000 I loved selling some one an expensive pair of shoes.  But the best was when they bought insoles and socks too!  Cha-ching$

But whats the deal with insoles?
I can't say I know a ton but I have a little insight.

We sold several different kinds.  Many brands were cheap and basically worthless.  They were just really soft foam that feel good in the store but probably made your feet/ankles/knees/back feel worse in the long run because they didn't actually provide support where you needed it.

Spenco seemed to be the real deal.  They seem well made and each variety addressed a specific purpose.

I was running a lot back then and tried a pair of Spenco insoles.  They didn't help.  They can't solve over training ;)

But they do seem to be very helpful for people with poorly formed feet.  Low or flat arches, severe over-pronation, etc.  For people with normal feet I'd generally say that a good shoe is all you need.  A real running shoe store sales person should be able to look at your feet and your gate and let you know where you fall on the spectrum of feet.

Also, doctors can make custom insoles but I have no experience with that.  I would certainly try the cheaper route of buying some $30 Spenco insoles first.

Warning: Insoles tend to take up more room in your shoes than a normal insole.  So be careful that you don't cause harm by wearing shoes that are too tight.  Adding insoles may mean that you need to adjust your shoe 1/2 size.