Right, here's what I've got - usefulness to be decided, but most of them sound practical.
Astrid - To do/task list organiser
Astro - File manager that lets you browse the phone/sd card - I'm sure this must be useful for something
cab4me - Choose where you are on the map (it'll try to work it out using network/GPS depending on your settings), then it'll give you a list of local taxi numbers. Grim... might want to install this one.
ConvertAll - A unit convertor that I'm probably going to uninstall in favour of handyCalc
handyCalc - ludicrously complicated graphical calculator that also does unit conversion
IM+ Lite - haven't really used this much, but it's the free version of an IM program that seems to support pretty much all the clients
Last.fm - Er, it's Last.fm
MapWeasel - Brings up a map of the uk with any traffic incidents highlighted, click on them for more details
Movie Finder - Local cinema listings with links to imdb pages
Nav4All - Someone on here (LaceSensor?) mentioned this. It's a satnav program, but I haven't had a chance to use it yet
Night Clock - Displays a clock on the screen, plays mp3s as alarm
Note pad - It's a pad. For notes
PktAuctions eBay - Links to all your eBay auctions (buying and selling)
Places Directory - Like Movie Finder, local listings for all sorts of stuff (banks, shops, parking, etc)
Power Manager - Uses different profiles depending on the power state of your phone (battery, low battery, ac, usb). The free version doesn't let you change the profiles
Ringdroid - Edit mp3s and use them as ringtones/notifications
Scoreboard - Supposed to keep you up to date with sporting results from pretty much any sports you can think of. I haven't tried it out properly due to lack of football.
Shazam - Play it music and it will tell you what it is. As has already been pointed out on here, this has to be the devil's work.
ShopSavvy - You've already got this, but for anyone that hasn't it allows you to search for products (either by typing in the name or scanning the barcode) and then finding the cheapest prices online and locally.
Shutter Speed - Supposed to offer a few more camera options, but I haven't had a chance to use it yet
SMS Popup - Lots of options to configure SMS messages
Sound Grenade - Just to amuse myself occasionally.
The Weather Channel - Weather
Twidgit Lite - A Twitter Widget, I only installed this yesterday, but it seems better than Twidroid
Twidroid - Twitter client
UK Traffic - Like MapWeasel, but just in text
Google voice search - Like Shazam, this use of technology scares me. The last time I saw any voice recognition software being used was about 10 years ago in PC World and it was laughably bad.