Thanks for the info about the reset, I have done as you have said by holding the home and power buttons for 15-20 seconds, once I done this I went to app stor and download a app and again it tells me about the 13 apps still waiting to download. As for the computer side of things, it shows that there are no updates and syncs with no problems to the phone.
I had this same problem, I think it happens when you try to update your apps through the iphone app store by selecting upadate all apps and then you lose internet connection or have a large app that your are trying to download via 3g. I tried syncing to my computer and reset which didn't work.
I finally fixed it by making sure I was connected to a good wifi connection then going back into the app store app on my phone, then went to updates and update all again. You then have to wait a while and don't leave the wifi area until all the apps are updated. This fixed it for me!
Here's how I solved the problem.
I have been unable to download app updates & new apps for about a week. To solve I
1. logged out of iTunes store
2. Closed all Safari windows
3. Closed all running applications by double tapping home-action key then holding down an app until I got the "-" circle above each. I then tapped the "-" circle on each app. (OBTW this can help save battery by closing background applications). I then tapped home-action key twice
4. I then went to Settings - General then at the bottom performed a RESET. I lost my screen wallpapers & alarm clock settings and had to re-enter my wifi passwords. Photos, contacts & browser history etc remained.
I was then able to download & install apps without any problem.
Best regards. OBTW this my first post even though I'm a know-it-all
OBTW just after I posted this Apple provided a software update to ios 5.1.1. You may want to update your iOS first & see if it solves the problem. If not, try mine. RM