My favorite pajamas for all three of my children are the PJ Pals from the Disney Store. They can also be ordered from Disney's website Disneyshopping.com. The generally run about $9.99 a pair but they are on sale frequently and can be purchased for as low as $3.99 at times, making them a very economical purchase for a good quality item.
I love that they are a lightweight cotton that washes and wears well. They have summer styles with shorts and short sleeved shirts as well as cooler weather styles with long sleeves and pants. They are snug fitting without being skintight. I do recommend that you buy at least one size up as they do seem to run smaller than many other brands.
The graphics change each season and usually feature all time favorites like Princesses and Mickey Mouse as well as the newest characters from the current theatrical releases. My kids love the characters and I love the quality, fit, and price of the pjs!