Doodlebug makes great card stock letter stickers. They stick well, but you can reposition them if needed. They come in great fonts and multiple colors. They are easy to mix and match; you can sub in another word (or letter) in another color and have the font stay consistent. I definitely get their letter stickers in many colors. Reasonably priced & great quality. My only complaint with this particular set is that I like to have both capital and lowercase letters in the same set, but that's a quibble.
I love all Doodlebug products because their colors always coordinate with all of their collections and products. These letter sets have NO UPPER CASE and look a bit whimsical, so they may not be appropriate for every craft project.