I don't know of any general POI data except what comes built in to garmin's map data.
A quick google has thrown this site up, which may be of interest
DOWNLOAD POIS :: GarminPOI.co.ukComment based on loading POIs into my 60CSx:
The way that "load your own" POI data works, you have to keep separate files for each category of POI you want. If you had them in the same file, you wouldn't be able to search for a bike shop. You would have to search everything nearby, and just scroll down the list until you spotted a bike shop.
As a result, all the files available are for a single type of POI, and must be downloaded separately. You put them all in the same folder, and upload them to the GPS in a batch using POILoader. This combines them into a single file (Garmin/poi/poi.gpi) on the GPS SD card, but using the original file names as category names.
Categories can be selected using the menu key from within the Custom POI search page.
There are a whole load of web sites offering POI files. The main problem with them is that many of the POI files in them are only partial - eg someone's started a file of UK campsites and given up after a couple of hundred, but uploaded what they have done for public use. Generally the complete ones are "official" - eg a POI file of all the MacDonalds Restaurants from McDonalds, or a paid for download of all GBG pubs from CAMRA.