I've spent a good bit of time testing apps and I've came up with the best solution for replacements for each stock app to give the phone the most functionality and diversity possible while still having stability and reliability.
The apps seen below replacing the stock apps increase functionality ten fold and allow for many more options and a greater user experience.
Scattered between the app store and cydia, these can be installed in seconds and you'll be loving your phone all over again. This list is compiled from all the apps available on the market to come up with the most solid solution. The qualifications were that these apps vastly succeeded the original apps without losing the ease of use or stability.
Give it a shot.
Below are the links to each item if you want to sit around on your butt and not have the coolest phone, but would rather read about everyone else's cool phone

most all of these are in the app store except for Dtunes, MXtube, and irealsms. (podcaster seen is also not in the store, but not exactly in the conversation, though you should get it!)
http://irealsms.com/screenshots
http://www.morninpaper.com/2008/12/d...oneipod-touch/
http://news.cnet.com/8301-17938_105-9991606-1.html
http://technologizer.com/2008/11/14/...weenies-dream/
http://www.clickapps.com/moreinfo.ht...section=IPHONE
http://vimeo.com/1424256?pg=embed&sec=1424256
http://www.snapturelabs.com/
http://www.iphonehacks.com/2008/11/iphone-dtunes.html
http://www.appleiphoneschool.com/2008/03/06/mxtube-10/
