So here is one I came up with that seems appropriate here (there is one and--I believe--only one answer):
CAMPING
+ HIKING
=KICKASS
Note that the sum of two single digits can result in either a single digit, or a two digit number beginning with 1, so to solve these one has to consider the possibility of "carrying" a one. For example, from the one's digits, we have G + G equals either S or 10 + S. Then, either N + N equals S or 10 + S, or N + N + 1 = S or 10 + S.
Also note in this problem, CAMPING and KICKASS have seven digits, while HIKING has only six, and so A + H has to carry a one, therefore C + 1 = K.
Usually with these, one can write a number of equations like those above, eliminating many possibilities. Eventually, one then has to try the different possible combinations until one works. Or, these days, one can "cheat" and write a computer program to go through and try every combination "brute force".

So if you're into this sort of game, have fun! I'll post the answer in a day or two.
Tom