Recovering images from Corrupt SD Card

I use class 10 SDCH cards in my Canon digital camera, but for some reason, the card reader on my relatively new computer doesn't read them. Because of that, I invested in a cheap USB SDHC card reader, which plugs into one of the USB slots on my computer.
This has worked without major problems so far, but now and again I get funny looking files on the card and sometimes my camera can't read the files after I have transferred them to my computer.
I should have taken this as a warning sign, as today I put the card and card reader into my computer and it said there were no files on the card, although the computer still shows that about 3gb of space has been used.
Unfortunately this seems to mean I have lost all of the pictures of the frosty conditions I took yesterday.
There seem to be a lot of software on the internet which claims to be able to recover corrupted files from SD cards but it's hard to tell which might be the best. Does anyone have any experience of using such software and possibly recommend which may be the most reliable?

I have not tried this but the supplier of this free software, Piriform, provide both Defraggler and CCleaner that I use regularly . Both those programs are widely reccomended . This software Recuva looks like it may do what you need re the card problems. http://www.piriform.com/recuva
Hope this helps.

Thanks LeoLion,
I have tried a couple of other free programs, Pandora and Zero Assumption Recovery, without success, although they do seem to be able to find files
on the disk which were never there in the first place!
I will give recuva a try and see if it is any better.
I suspect however that I have all of my "frost" images for this month!

Wow!
I spoke too soon, ZAR now seems to have found the images which it couldn't find yesterday.
Actually, yesterday it couldn't even find the card at all!
I will still give recuva a try however.

I tried recuva but unfortunately it didn't find the files, but then neither did ZAR the first time I tried it.
It did find some files which were never on the SD card, like Pandora did, which I can't understand.