A flash which simply sits in the hot shoe pointing forward offers little more than what one gets with a built-in flash. In fact, since the Pentax AF200FGZ does not work as an optical wireless P-TTL controller, it is actually a step back in features from the built-in flash on most recent Pentax camera bodies.
All other models covered here can tilt upwards, enabling ceiling-bounced flash for indirect, even lighting.
The Tumax DSL28 and very similar Metz 24 AF-1 are quite compact flashes, requiring only two AA batteries. Most tilt-capable flashes follow a design where they are hinged in the middle and the entire head of the flash tilts. On these, just the flash reflector tilts on a small hinge (see the picture here). It's very like Nikon's SB-400 Speedlight — and to editorialize a bit, a lead Pentax should follow when they get around to updating the AF200FGZ.
The Pentax AF360FGZ, Tumax DSL88 series (including Metz 36 AF-4/AF-5), and Promaster 5250DX, 7200EDF, and 7400EDF can tilt upwards to 90°, but don't have the ability to rotate from side to side. The other models can both tilt and swivel from side to side, which is vital when using ceiling-bounced flash with the camera in portrait orientation. Of course, if your primary use of the flash is off-camera, side-to-side swivel is unnecessary.
The Pentax AF360FGZ can tilt down to -10°, and the Promaster and Sigma models to -7° — this gives better coverage of close subjects. The Metz 58 AF-2 can tilt downward by 7° as well, as could the older 48 AF-1 and 50 AF-1 models, but the newer 44 AF-1 and 52 AF-11 have no downward tilt. Tumax models also have no downward tilt ability.
All the Pentax, Metz, Promoster, and Tumax models have click-stops at 0°, 45°, 60°, 75°, and 90°, which is quite convenient if you want to direct some light forward (and recommended when using a diffuser accessory like the Sto-Fen Omnibounce). The older 530-series Sigma models only click into place straight forward and straight up. The newer 610-series models are better, missing only the 45° option from the typical list.