The Canon EF 70-200mm f4 IS USM L lens is a professional grade 70-200mm lens without the size and heft, as well as price, as found in f2.8 versions.
You get you what you pay for with the Canon EF 200-400mm f/4L IS USM Extender 1.4X: superlative performance and flexibility.
A midrange Zeiss and 5.8x power zoom fill some holes in the E-mount lineup.
The 55-250mm f3.5-5.6 STM fills a big hole for the dual-lens kit devotees of the company's latest Rebel models.
It's a great option if you have a shelf full of K-mount lenses and don't mind missing some action shots, but the Pentax K-01 isn't such a great option for a typical amateur photographer.
The Fujifilm X-T1 is a great camera for advanced photographers as long as its quirks don't bother you.
Cheaper and with better photo quality than its sibling, the Sony Alpha DSLR-A500's quirky design is the only real flaw in an otherwise solid entry-level model with fast Live View shooting and a useful tilting LCD.
If you're a Live View-oriented shooter who doesn't care about color accuracy, the Sony Alpha DSLR-A550's good performance and decent noise profile make it attractive for the money. Otherwise, you can find a better camera.