Which cassette do I have?

fauxpas said:

The tiny print on the cassette says 'Shimano HG' and further around says 'Hyper Glide'.

Is this the cassette? Hyper Glide? Is it any good?

I was expecting to see sora or tiagra or 105.

Do cassettes come in sora tiagra or 105?

All modern Shimano cassettes are HyperGlide regardless of their group level. Just their tradename for the ramping system (predated many moons ago by Uniglide). If your cassette has the stock lockring, it should have the cassette part number stamped on it (some DA will have also DuraAce stamped on it). For example:
If it says CS-6600 or 6500, CS-HG90 it is Ultegra;
CS-5600, CS-HG70 is 105 Level;
CS-HG50 is Tiagra/Sora/Deore

It says CS-HG50... so that means avg...

fauxpas said:

It says CS-HG50... so that means avg...

Yes, average, but will perform just as well as the more expensive brethren. The major difference with the higher priced ones is that they are lighter and better finished. The cassette is one place where bike manufacturers sometimes save some money by using a lower grade cassette with otherwise higher level groups. I would use the HG50 until it is worn, then consider an upgrade. 105 is the best value in the Shimano line-fully compatible with other groups, decent finish quality, and much cheaper than Ultegra or DA with near equivalent performance.

I've noticed the varying ratios offered between the cassette I have and those on offer on ebay.

I will wait till this cassette dies and go 105 to match the derailluer.

Currently, the lowest rear gear (biggest sprocket) is just low enough for me to pump up a short but ferociously steep hill just before I get home. By the time this cassette dies, I hope to be able to use a higher gear on the same hill, then that will enable me to look at more cassettes on offer without being too worried about the low ratio...

Just spotted a HG50 on ebay (aus)... he says its an ultegra... hmmmmm

fauxpas said:

It says CS-HG50... so that means avg...

Faux Pau if you have a 9 speed cassette the CS-HG50 is Tiagra, if its 8 speed its Sora.

http://www.shimano.com.au/catalog/cycle/products/component.jsp?PRODUCT%3C%3Eprd_id=845524441762505&FOLDER%3C%3Efolder_id=2534374302037406&ASSORTMENT%3C%3East_id=1408474395181400&bmUID=1155127058718

Ahhhh, k... she's a 9 speed...