The following links contain various applications I've collected or installed. Most of them are freeware, some are commercial programs that have some sort of restriction until registered. All these programs are readily available elsewhere on the internet, I've simply put the ones I use in one place. If it's not listed, I don't have it.
Google Maps Application 3.2.0 (1mb):
GoogleMaps.CAB
Google maps application.
Google Search Application (184kb):
GoogleSearch_signed.cab
Google Search application for the today screen.
Live Search (1386kb):
LiveSearchWM6.CAB
Windows Live Search.
Or is it called Bing now?
Bing (1380kb):
BingWM6.CAB
Windows Live Search / Bing.
MSS Converter (1.4mb):
MSS Converter.CAB
The software is easy to use. You can set the units to show or hide. Convert between lengths, areas, volumes, masses, speeds, temperatures, pressures, times, angles, energies, powers, radiations, forces, angular speeds (and frequencies), computer units, viscosities, luminosity units, magnetism, torques, etc, etc.
My Mobiler (490kb):
MyMobile123_06152008.zip
View your mobile screen on your desktop.
Control your mobile by using desktop keyboard and mouse. Copy/Cut/Paste text between mobile and desktop. Capture mobile screen. Drag and drop files to your mobile. Support ActiveSync / IP Connection. Support Mobile Explorer (File Browse). I used this program to take all the screen shots I used on these pages. More info from >> www.mymobiler.com/
FDC Soft Task Manager V3.1 (226kb):
FdcSoft TaskMgr wm2005_3.1.cab
A great task manager and registry editing program. - Process Manager, CPU Usage, Service Manager, Device Manager, Windows Manager, Notification Manager, IP Config, Ping, Net Stats, Registry Editor by FDC Soft - www.dotfred.net
FDC Soft PIM Backup V2.8 (372kb):
PPCPimBackupV2.8_wm2005.zip
A great tool for backing up and restoring PIM before and after a hard reset. The PIM backup application is a tool that allows to backup/restore personal information stored on windows mobile based pocket devices. Contacts, appointments, tasks, messages, calls. This is also from FDC Soft. - www.dotfred.net
PHM Soft Reset (1kb):
PHMSoftReset.CAB
Soft reset your mobile device without having to use the power button. More info from >> www.phm.lu/products/PocketPC/PowerToys
SK Tools 5 (4.4.7.9)(1227kb):
SKTools5.CAB
This multi-function application includes more than 50 tools and allows an easy but powerful maintenance of Windows Mobile devices. Clean up your registry and file system, free-up RAM, backup and restore, find duplicate contacts, appointments and tasks. SKTools can manage installed applications, Today plugins, software keyboards. From s-k-tools.com
Xperia Tweak V2.0 (675kb):
XperiaTweak2.CAB
This is a great utility for tweaking some settings on the Xperia. Visit the Authors site for more information www.cliffords.nu/
GPS Cycle Computer (952kb):
GpsCycleComputer_3.103.CAB
A nice GPS tracking program, export to KML and GPX files. By AndyZap.
Handy Shopper (426kb):
InstallHandyShopper.msi
A handy shopping list program. (Can be used for lots of other things as well, music catalogs, book lists, movies, etc, etc) Visit HS3 for more information.
Facebook Application (871kb):
Facebook_v1.0.0.7p.CAB
This isn't a bad Facebook application and it has some nice features.
Stuff from xda-developers.com:
SdkCerts.cab SDK Certificates need to be installed to be able to install some of the CAB files.
XperiaCamera_R3__R27-35059_.cab Xperia Camera. Read about it here >> [APP] XPERIA R3A CAMERA with AutoFlash & GeoTag: CAB installer

OEM_SE_XPeria_Keyboard.CAB This is the new finger friendly software keyboard released with the R3AA ROM's. There are a lot of options available. It has XT9 features, pre-emptive text and next word choice. You can choose between a QWERTY layout, or a traditional phone keyboard layout for easy single finger text messaging etc. A help file is installed with it. I learnt about the file in this thread: R3AA ROM XT9 Keyboard and other stuff (from itje's rom extracts)

Spike's_ MicNeo_TaskBar_Xperia_Varient_1_v2.cab The task bar as seen in my screen shots.
Not happy with the Volume of your Xperia? : Either one of these files will fix it. They will make the volume louder. You only need to install one of them.
Initially I installed the optxperiabeta02.cab but apparently it tweaks some other settings too. Exactly what and why, I don't know. I noticed no ill effects though. After doing a hard reset, rather than re-installing the optxperiabeta02.cab I installed the Audiopara.cab. All it does is replace two .csv files in the windows directory without tweaking anything else.
(If you install the optxperiabeta02.cab and want to uninstall it, it appears as "Auanti by Davide Gialli OptXperia").
edit: I found more info in this thread here:: xda-developers.com