I have an older Olympus micro-cassette recorder that has served me well for about 15 years. I used it recently to make verbal notes while looking at houses. Of course, I was not trying to use it "concealed" in any sense.
I know there are a number of digital voice recorders that are smaller and perhaps more suited to your application. Of course, Sony appears to lead the market in this arena. This [url=http://www.sonystyle.com/is-bin/INTERSHOP.enfinity/eCS/Store/en/-/USD/SY_DisplayProductInformation-Start;sid=bsZNN9HkD2pNPu8BmTNHPJ7rss5xdsisayc=?CatalogCategoryID=W5gKC0%2eNvgEAAAD1N9xN_bDM&ProductID=RcwKC0%2eNvSYAAAD12yZN_bDS&Dept=pa]LINK[/url] is for a rather spiffy number that uses Memory Sticks. It can plug into your PC, and using the provided softwar can transcribe the recording into text! $300, but nevertheless nifty. You might trot down to your local Office Depot, Staples, or whatever, to play with the ones they have on display.
Good luck.