Sally one effective and very easy way of dealing with sensor dirt is pre-treated swabs that are already wet with the right amount of solvent so you need to open one pack at a time, clean and throw the swab away. Here is a link
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This is the cheapest yet effective therapy. I have personally used this one and found it easy and effective. When ordering pay attention to the width of swab. If you have full frame DSLR, you need 24mm and if factored sensor (Such as D40) you need 17mm version.
You can't beat this one on price and comfort, combined.