Professional labs use miniature can openers to avoid getting any fragments into the package since failure analysis may want to see if the device failed from particulates. For RE purposes a Dremel can suffice followed by a good clean.

http://www.youtube.com/watch?v=lt_zFq4qzd0

Ceramic-metal lids can also be removed with a torch. However, it is easy to warp the ceramic package making it difficult to get a good image of the die.

Sometimes dies are soldered to a substrate (eg: silver heatsink / carrier). Example after die was removed (by force):

Note the raised corners. This means that without completely melting the solder it is hard to get loose. Soak in nitric acid and it should quickly dissolve and come loose:

Of course, it might take a while to get under the entire die. Heating without will help to get it off but I have found that it can take a lot of force to move even with solder melted and so its best to chemically remove as much silver as possible first.