I'm after a circular polarising filter (for a 58 mm lens) just in case we ever get a day with blue sky again. Jessops sell them at about £35, Curry's and Argos at about £20, and eBay from about £2 so what should I go for? Am I likely to notice any difference between the cheapest and the most expensive?

Depends what lenses you are using the CP on.

If you are using £500 lenses I personally would spend more than £2 on a CP or indeed any filter.

The glass and coating used on a well known branded filter are going to be better than an unbranded low cost filter.

Also depending on the depth of a filter (especially with polarising filters, being so deep) you may get some vignetting of your images.

Well no, it's the Canon kit lens with the EOS350D actually, so I'm getting the feeling mid-range might be appropriate.

Here you go:

http://www.t4cameras.co.uk/index.asp?pname=/moreinfo.asp?id=2035

or

http://www.bristolcameras.co.uk/p-circular-polarising-filter-size-58mm.htm

I've used both suppliers and will use them again.

Cheap filters are useless - the loss of quality is tremendous. Look for B+W, Hoya (black series), eventually Marumi (very good and quite cheap filters). If you want the best, go for Heliopan. Ebay is your place :)

Thanks for that everyone.

you can buy hoya filters from ebay for a good price

Dramatic Peak District Photos: www.peak-photos.co.uk