So far KSP 0.15 is fantastic. I hesitated to try my hand at space planes, but once I gave it a shot I was hooked. The possibilities are endless. Not only do you have many types of engines to choose from, you can combine parts from rockets too.

• A jet fighter with boosters? Check.
• An orbiter that starts on the back of a space plane? Check.
• Vertical take-off jet using engines pointed down? Check

Here are a few designs to get you started. (Download links below pictures)

Cripply

Banshee

Kerbal Interceptor Fighter

Kerbal Strike Fighter

Taxi

MiG-29 (Thanks to zombiphylax)