My hair's not as thick as I would like but I find the rainforest volume shampoo from The Body Shop is amazing. It does what it says on the tin and gives me good volume and actually makes my hair seem so much healthier and it's also good with regards to the chemicals they put in it (I don't know much on this but I know that it has no sulphates and that's good - a little bit of research would tell you more). Also, I'm now working on my diet and what I put into my body - i.e. having more water, more protein (as hair is made of protein so a good diet with sufficient protein is key) and just more green veggies. I've just had this wake up call so I don't know how long it will take to show effect but I'm determined to stick to it so maybe focusing on diet is something you could do too but until then, good products can help.
Also, when I wash it, I don't blowdry it if I can help it and usually keep my hair upside down while it dries i.e. lying on the sofa and letting the hair hang off the edge, if that makes sense. Helps with becoming a bit more volume-y.