Here are 3 resources ordered by read-time length:

The Lambda Calculus for Absolute Dummies (like myself) : http://palmstroem.blogspot.com/2012/05/lambda-calculus-for-a...

A short introduction to the Lambda Calculus: http://www.cs.bham.ac.uk/~axj/pub/papers/lambda-calculus.pdf

Lambda Calculus - Step by Step: https://www.dropbox.com/s/i0qgfoye6artcp8/untyped_lambda.pdf...

I enjoyed Benjamin Pierce's book Types and Programming Languages:

https://www.cis.upenn.edu/~bcpierce/tapl/

He provides theory and code that starts from untyped lambda calculus and progresses to typed lambda calculus, system F, and higher-order system. Note, the article above was written by Barendregt who summarized high-order systems in terms of the "lambda cube". The Pierce book provides enough theory and context to understand why that's important by the time he gets to it in chapter 30.

David Beazley just gave a tutorial on Lambda Calculus at PyCon, definitely worth the 3+ hours https://youtu.be/pkCLMl0e_0k

The Computerphile segment is pretty good:

https://www.youtube.com/watch?v=eis11j_iGMs

If I might plug my own work:

I did a 5-part lesson on my blog. It starts from zero knowledge and ends up with two Fibonnaci calculators (one recursive, one iterative):

http://blog.suspended-chord.info/tag/lambda%20calculus/

(There's also a theorycrafting post I did a bit later to build a rudimentary object-oriented programming paradigm in the Lambda calculus.)

I really like Lambda Explorer [0]. It's an in-browser interactive tutorial that does a good job of nudging you towards the next idea so you can discover it yourself, but it's there with a solution if you get stuck.

[0] https://lambda-explorer.net/

Henk Barendregt, the author of this paper, has an excellent reference book on the untyped lambda calculus called "The Lambda Calculus: Its Syntax and Semantics". I believe he also wrote a book on the typed lambda calculus but I have never read it. This is a good reference text, but in my opinion is not a good introductory text.

For a good introduction, I would recommend J. Roger Hindley's introduction to the lambda calculus and combinatory logic entitled "Lambda-Calculus and Combinators: An Introduction". It includes some interesting info on SKI combinator calculus in addition to the lambda calculus.