Free ice water from most counter spots. It sounds corny, but in the summer, free cold water is the best thing!
Our family thinks the Silhouettes are a good Disneyland souvenir. We try to do them every couple of years to show our DD growth. We have them from our childhood and now are adding hers to the collection. The best thing is that it says Disneyland, not Disney Parks! Without the frame they come in at around $9 plus tax for two copies. We usually do not purchase the frame as we have our own frames for them. They will hold them for the end of the day, so you do not have to carry them around. One of my Disney magical moments was having my DD's first one done by the same lady who did mine when I was a child!
Here You Leave Today and Enter the World of Yesterday, Tomorrow, and Fantasy.
“To all who come to this happy place; welcome. Disneyland is your land. Here age relives fond memories of the past...and here youth may savor the challenge and promise of the future. Disneyland is dedicated to the ideals, the dreams and the hard facts that have created America...with the hope that it will be a source of joy and inspiration to all the world.” - Walt Disney, Disneyland Opening Day Speech 1955
I think the souvenir steins/goblets at Maurices (Fantasy Faire) are reasonable. Then again, I'd spend almost anything for the apple boysenberry freeze that comes in them. There are clip-on ears for under $10, but they dont stay in very well. Occasionally, you can find decent sales in the shops, shirts or purses for under $20, you just have to look long & hard.
We splurged this last trip and stayed at the DL Hotel so we got some "free" stuff. We got luggage tags (4), one ride photo, 4 pins and 4 lanyards, and deals on Ridemakerz and some other offers we didn't make use of. Not cheap stuff within the park but just thought I'd mention it for information sake.
Nothing can really beat the merch at the character warehouse about a mile away from the park...some of what they have is Godawful but I've found last year's ear hats, keychains, shirts, lanyards and other goodies there for very reasonable prices.
Within the parks the cheapest thing I've found: they have little buttons with character artwork for $1.25 at some of the checkout lines (I have seen them at the Emporium and the shop by Winnie the Pooh). I found a really keen Maleficent button, and they had a lot of other characters, like Alice, the Cheshire Cat and the Evil Queen.
You'll see these by the cashier in the Emporium and the little vendor cart by the old Fantasyland Station for the skyway. The little buttons, not pins, buttons with characters on it. It is like not even a dollar each, but fun to put on your Mickey ears or your backpack. They have different buttons like every 6 months or every few months right?
But that is something that is really cheap to get especially with an AP!