I'm a amateur web developer and I discovered codecanyon.net which is also part of the same marketplace as themeforest.net, videohive.net, etc. They have all kinds of scripts and apps that one can download and use and I highly recommend it for anyone (especially if you're not quite ready, like me, for developing everything from scratch). The prices seem reasonable, I wouldn't really know because this is the first such site i've found. If anyone out there has other sites that they know of i'd appreciate hearing about them, but this codecanyon.net site really suited me well. The service I got was excellent and the site itself was easy to navigate for a first time visitor.