Here's a wealth of information that I found useful for learning to implement mixed models in SPSS.
My favourite book on statistics is the latest version of Andy Field's "Discovering statistics using SPSS" and his website ("Statistics Hell") is an excellent, albeit unorthodox, resource! The chapter on mixed models has a couple of typos to navigate.
Bristol's Centre_for_Multilevel_Modelling is outstanding. I attended one of their courses - it was excellent.
The UCLA website has some great resources for SPSS: Repeated measures analysis with SPSS, Using SAS Proc Mixed to Fit Multilevel Models, Hierarchical Models, and Individual Growth Models, How to obtain pairwise comparisons of effects and interactions.
David Garson's Statnotes are also very thorough. Linear Mixed models.
Here are some key resources:
Singer, J. D. & Willett, J. B. Applied Longitudinal Data Analysis. (Oxford University Press, 2003).
Singer, J. Using SAS PROC MIXED to Fit Multilevel Models, Hierarchical Models, and Individual Growth Models. Journal of Educational and Behavioral Statistics 24, 323-355, (1998).
Although the last reference deals with SPSS, you can learn how to implement this in SPSS thanks to UCLA, John Painter, and Craig Enders and James Peugh via "Using the SPSS Mixed Procedure to Fit Cross-Sectional and Longitudinal Multilevel Models. Educational and Psychological Measurement 65, 717-741, (2005)" and SPSS Mixed: ‘Point and Click’.
Here are some other important references:
Rubin, L. H., Witkiewitz, K., St. Andre, J. & Reilly, S. Methods for handling missing data in the behavioural neurosciences: Don't throw the baby rat out with the bath water. The Journal of Undergraduate Neuroscience Education 5, A71-A77, (2007).
Landau, S. & Everitt, B. S. A handbook of statistical analysis using SPSS. (Chapman and Hall/CRC, 2004).
Heck, R. H., Thomas, S. L. & Tabata, L. N. Multilevel and longitudinal modeling with IBM SPSS., (Routledge, 2010).
Krueger, C. & Tian, L. A comparison of the general linear mixed model and repeated measures ANOVA using a dataset with multiple missing data points. Biol Res Nurs 6, 151-157, (2004).
Gueorguieva, R. & Krystal, J. H. Move over ANOVA: progress in analyzing repeated-measures data and its reflection in papers published in the Archives of General Psychiatry. Arch Gen Psychiatry 61, 310-317, (2004).
Chan, Y. H. Biostatistics 301A. Repeated measurement analysis (mixed models). Singapore Med J 45, 456-461, (2004)
Chan, Y. H. Biostatistics 301. Repeated measurement analysis. Singapore Med J 45, 354-368; quiz 369, (2004).
SPSS. Linear Mixed-Effects Modeling in SPSS: An Introduction to the MIXED Procedure (this is the newer version).
Bickel, R. Multilevel analysis for applied research. (Guilford Press, 2007).
West, B. T., Welch, K. B. & Galecki, A. T. Linear mixed models: a practical guide using statistical software. (Chapman and Hall/CRC, 2007). See also their website for implementing these via SPSS.
Miller, G. A. & Chapman, J. P. Misunderstanding analysis of covariance. J Abnorm Psychol 110, 40-48, (2001).
West, B. T. Analyzing longitudinal data with the linear mixed models procedure in SPSS. Eval Health Prof 32, 207-228, (2009).
Click here to view a tutorial on Linear Models that I have developed for analysis of longitudinal data obtained using animals.