We use a lot of sensory/tactile experiences to extend our letter learning. Here are just a couple of my favorites:
Building letters with Legos (L, T, and I are especially good for this medium). My kids went crazy and tried to build the tallest L. You can also do this with blocks, snap cubes (kind of like unifix blocks, but with more flexibility), tinker toys, etc.
Play dough letters - free form, or use alphabet cookie cutters. We also make them with bread dough and create "pretzel letters". Many versions of playdough letter mats are freely available on the internet.
Magnet/Marble Letters - These are the little sticks with magnets on each end and little metal balls that stick to them. I got these at the dollar store, and they work ok (the magnets are a little wimpy). I prefer the Magz brand "magnetic construction toy" but they are a little pricey. CAUTION: do not allow children to put in mouth. They are not as dangerous as the "bucky balls" since the balls are not magentized and the magnets are firmly attached to the plastic sticks. The kids LOVE these!