I'm aware of the unsolvable puzzle task and have access to some versions of it. However, I wonder if that's the best way to go about measuring cognitive depletion because this task in itself is depleting.
Béatrice Marianne Ewalds-Kvist has already written about the very good overview from Hagger et al.
You can also look at this meta-analysis:
Duckworth, A. L., & Kern, M. L. (2011). A meta-analysis of the convergent validity of self-control measures. Journal of Research in Personality, 45(3), 259-268.
Jian-Bin Li has recommended the Stroop task to you. It is used very often and you can change the difficulty level quite easily (modified stroop task, proportion of congruent stimuli, verbal vs motoric responses etc.). If you want to read more about this then I recommend an exaustive review from MacLeod.
MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109(2), 163-203.
There also other measures: motoric inhibition, delay of gratification (sweets, alcohol, smoking), Wisconsin Card Sorting Task. white bear test etc.
Sometimes the Heart Rate Varability can be used to indicate an ego depletion effect (changes between the two tasks). But you must have a device to be able to measure HRV. Furthermore I have to stress the word 'sometimes' as I have seen unpublished studies, where there was no connection. However, if you're interested in physiological measures then it's one possibility. Nevertheless you still need a task requiring self-regulation.
Baumeister, R. F., Vohs, K. D., & Tice, D. M. (2007). The strength model of self-control. Current Directions in Psychological Science, 16(6), 351-355.
Geisler, F. C. M., Kubiak, T., Siewert, K., & Weber, H. (2013). Cardiac vagal tone is associated with social engagement and self-regulation. Biological Psychology, 93(2), 279-286.
Using the Networked Fire Chief for ego-depletion research: measuring dynamic decision-making effort and performance.
Barber LK, Smit BW.
Abstract: This study replicated ego-depletion predictions from the self-control literature in a computer simulation task that requires ongoing decision-making in relation to constantly changing environmental information: the Network Fire Chief (NFC). Ego-depletion led to decreased self-regulatory effort, but not performance, on the NFC task. These effects were also buffered by task enjoyment so that individuals who enjoyed the dynamic decision-making task did not experience ego-depletion effects. These findings confirm that past ego-depletion effects on decision-making are not limited to static or isolated decision-making tasks and can be extended to dynamic, naturalistic decision-making processes more common to naturalistic settings. Furthermore, the NFC simulation provides a methodological mechanism for independently measuring effort and performance when studying ego-depletion.
Using the Networked Fire Chief for ego-depletion research: measuring dynamic decision-making effort and performance.
Barber LK, Smit BW. J Soc Psychol. 2014 Sep-Oct;154(5):379-83. Method: Networked Fire Chief for ego-depletion (NFC). Ego-depletion led to decreased self-regulatory effort, but not performance, on the NFC task.
Psychol Bull. 2010 Jul;136(4):495-525. Ego depletion and the strength model of self-control: a meta-analysis. Hagger MS, Wood C, Stiff C, Chatzisarantis NL.
Proc Natl Acad Sci U S A. 2013 Sep 10;110(37):14837-42. Beliefs about willpower determine the impact of glucose on self-control.
Job V, Walton GM, Bernecker K, Dweck CS.
"....people who view willpower as plentiful (a nonlimited resource theory) showed no benefits from glucose--they exhibited high levels of self-control performance with or without sugar boosts"......
I recommend the Stroop task, which has been demonstrated to effectively and efficiently manipulate self-control resources. Please bear in mind that the distinction between depletion and non-depletion may be dependent on how many trials the participants are going to take and also on the ratio of incongruent and congruent trials.
Béatrice Marianne Ewalds-Kvist has already written about the very good overview from Hagger et al.
You can also look at this meta-analysis:
Duckworth, A. L., & Kern, M. L. (2011). A meta-analysis of the convergent validity of self-control measures. Journal of Research in Personality, 45(3), 259-268.
Jian-Bin Li has recommended the Stroop task to you. It is used very often and you can change the difficulty level quite easily (modified stroop task, proportion of congruent stimuli, verbal vs motoric responses etc.). If you want to read more about this then I recommend an exaustive review from MacLeod.
MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109(2), 163-203.
There also other measures: motoric inhibition, delay of gratification (sweets, alcohol, smoking), Wisconsin Card Sorting Task. white bear test etc.
Sometimes the Heart Rate Varability can be used to indicate an ego depletion effect (changes between the two tasks). But you must have a device to be able to measure HRV. Furthermore I have to stress the word 'sometimes' as I have seen unpublished studies, where there was no connection. However, if you're interested in physiological measures then it's one possibility. Nevertheless you still need a task requiring self-regulation.
Baumeister, R. F., Vohs, K. D., & Tice, D. M. (2007). The strength model of self-control. Current Directions in Psychological Science, 16(6), 351-355.
Geisler, F. C. M., Kubiak, T., Siewert, K., & Weber, H. (2013). Cardiac vagal tone is associated with social engagement and self-regulation. Biological Psychology, 93(2), 279-286.
Cognitive depletion measurements can be easily identified by the relative capability of decision making and volition control. Lacking decision making capability, and volition control on a simple to complex program can determine the levels of cognitive depletion from the minimal to devastating--or dysfunctional--non-functional levels being the extremes.
"One of the most powerful and dramatic features of human psychology is the capacity for volition, including choice and self-regulation. Recent work has suggested that self-regulatory operations consume a resource that is depleted afterward. When people override their responses, they are subsequently less successful at controlling themselves or responding actively, even in a seemingly unrelated sphere of activity (Baumeister et al., 1998, Muraven et al., 1998, Vohs and Faber, 2007 and Vohs and Heatherton, 2000). The implication is that some resource akin to energy or strength is expended in these processes, creating a state that has been dubbed ego depletion."
Journal of Experimental Social Psychology
Volume 43, Issue 3, May 2007, Pages 379–384
Try as I may this may not be what can help. Aloha!!
Following Lukasz Stasielowicz's suggestion to examine (real time) heart-rate variability, I would add the work of Alan Watkins in commercializing it as a basis for his executive leadership coaching. His demonstrations use a simple blood oxygen sensor which may be clipped to one ear and connected to electronics which display O2 levels in near real time:
Dr. Alan Watkins - Complete Coherence (UK).
http://youtu.be/q06YIWCR2Js TEDxPortsmith talk Part I (demo at t-14 mins)
http://youtu.be/Q_fFattg8N0 TEDxPortsmith talk Part II
http://www.complete-coherence.com
http://www.coherence-book.com (not an academic treatment, but contains many academic references)
To this I would also add NASA's Task Load Index (NASA-TLX) which I am aware of as a multidimensional assessment tool. No studies that use this tool come to my mind, but perhaps it can become a basis for one of your literature searches.