Here are some links to find resources for your Sony Ericsson mobile phone.

Themes, Wallpapers, Screensavers :
Lasyk is the best website I can recommend for downloading free themes, wallpapers, and screensavers for your SE mobile. This site also has a few games and applications. The best things are the themes and walls ofcourse, you can find a wallpaper of almost everything in this site.If you have a k750, goto . If you have a k800 goto . You get the idea now?

General info and help : is a site that is rich is resources for SE fanboys (I'm one myself!). Here you can find the latest news, rumors about upcoming models, a lot of useful links, etc. There is a really good Forum that can be a good source of info. If you wanna modify your mobile a little, be sure to check out the forum. With the help of this forum I've modded my k750 beyond recognition:)
Esato is another SE-related site. The forum has been around for some time, which means that it is quite content-rich.
TopSony forums is another forum site rich in info. There seem to be quite a few experts in this site.

Related post : Free content for Nokia mobiles.