This will be the third year of having my above ground pool - so far I just have had the pump wired to a switch in my garage which I'd have to remember to turn on and off each day, and with my work schedule forgot half the time. I'm looking for some sort of simple, inexpensive 24 hour timer which a manual On/Off switch for if we use the pool during times the pump isn't scheduled to run, I can switch it on without interrupting the timer schedule. The line from the breaker box is dedicated to the pump only, on a 20Amp breaker. I'd also like this to be a hard wired timer I can mount on the wall inside my garage. I really like the Mechanical Time switches (like the hot water heater timers) but I can't seem to find any 20Amp ones with a manual On/Off switch.

Anyone have any ideas?

Thanks.

Does anyone else think that a simple Intermatic timer would be the ticket here?

I sure do! Don't know the model numbers, but what I have is as basic as it gets, and would fit the bill. It's just a pretty basic intermatic clock timer.

Here you go...

http://swimmingpooltimeswitch.com/CD-104P.html

Not saying that this is where to buy it or anything, but this is the simple Intermatic Mechanical Timer.

That's the timer we have. Two ON/OFF tabs and a manual override. We've only ever used one ON/OFF setting, haven't had a need for two. It runs during the night hours. When we swim in the afternoons I flip the lever to ON and then either just leave it running or I turn it back off when we're done. It's a very handy gadget.

That's the ticket.

The picture omits the fact that there's a cover over those bare terminals after you get it all connected.

I have timer that i bought from lowes.
Something like this, just make sure it will carry the AMPS of the pump motor.
http://www.lowes.com/pd_155550-207-TM13DOLBL_0_?productId=3125317&Ntt=timer&Ntk=i_products&pl=1&currentURL=/pl__0__s?newSearch=true$Ntt=timer$y=0$x=0

So you would have to cut the plug from the end of the cord and wire it to those terminals?

Most pumps for AG pools are 110v, and don't need 20 Amps. I would be concerned if you have a 20A breaker wired to 14 G wire, that is a code violation (and a fire hazard.) Most light switches are only rated for 15A, as are most duplex outlets.
You should be able to find an in-expensive 15A timer, especially if it is in an indoor location. The simplest moving clock-face tripper light timers ($5) are rated for 15A, and most have a manual on/off wheel. Same principle as the intermatic ($60) pictured above.
Good Luck, and Best Wishes!