Last Fall, Twitter began adding support for geolocating Twitter posts (Tweets). This is an opt-in feature of Twitter, that you must enable. To enable this feature, log in to Twitter and select "Settings" in upper right corner. Under the "Account" tab, check the box for " ". This will allow Twitter.com (image 1 - note the toolbar at top requesting to use my location) or third party apps to distribute your location with each Tweet. More details, privacy info, and an F.A.Q about "geotagging" Twitter posts is available from Twitter.
GPSTwit (not to be confused with GPSTweet whch Tweets your position only). At $.99, this little app allows you take a photo, include a Tweet, optionally geotag, and post a Tweet to Twitter. The image is displayed on GPSTwit.com, along with other images. Recently I posted a picture of downtown Denver during the ISTE 2010 conference (#ISTE10).
It's fast, simple and works great for geotagging text or text+pic.