I’ve found the easiest method is a combination of the Formlabs spatula and a razor scraper for glass. Something like this: http://www.platinumsupplycorp.com/View/Allway-Glass-Scraper-Razor-Scraper-07007
What I do is I wedge the razor scraper under the part just a little; the razor won’t travel too far because of the handle. Then I leave the razor there and take the spatula and wedge it between the razor scraper and the build platform. Once the spatula is under the part, I remove the razor scraper and the spatula moves under the part a lot more freely. The razor doesn’t have to go under all the way, it just has to go enough under to get the spatula started. For tough parts, a little wiggling around a corner works best. Don’t use too much force or you could injure yourself or damage the part, and once it gets going it doesn’t take too much effort to get the razor under the part.
If you can find a glass razor scraper with a larger handle, it will probably give you a little more leverage. I bought two, one with a really tiny plastic handle (like this one: http://goo.gl/edeyU), and one like I linked to above. The small plastic handle one gave very little leverage and was essentially a waste of money. They also sell razor scrapers with wide blades (http://goo.gl/0z9ud), but I avoided that one because a longer blade means more chance for personal injury, and it wouldn’t be any more useful than the smaller one since the blade won’t go very far under the part anyway.
If you go with the glass razor scraper, be sure to wash off the blade before you use it; I believe most (maybe all) of the blades used in this style of scraper come oiled so they don’t rust (and they do rust quickly). You don’t want this on your build platform or in your resin. After you use it, rinse the tool off in the alcohol bath and wipe it dry, or any resin not rinsed off the tool may cause it to be a little gummy or slippery on your next use. Don’t leave the tool in the alcohol bath or the blade will eventually rust, and it seems it can start rusting in less than a day (this is with 91% isopropyl alcohol, higher purities may not rust it as quickly).