For some flashes, a wide angle diffuser is a built-in feature. The Promaster flashes don't have that, but the 5750DX and all the 7000-series models include a push-on plastic diffuser in the package. Be aware that this isn't meant to be a light softener or even to provide a bare-bulb effect like a Sto-Fen diffuser — the point is to spread out the flash's coverage for wide angle lenses
A soft carrying case is included with all Pentax and Sigma models, and with the Metz MZ 54-4i and 58 AF-1/AF-2. The Tumax DPT3 and DPT5 flashes usually have this too, but some rebrandings may not.
The Pentax AF540FGZ, Metz 58 AF-1/AF-2, Sigma EF-530 DG and EF-610 DG (both ST and Super), and Promaster 7500EDF models all come with a flat plastic stand to hold the flash on a table or other flat surface for off-camera operation. This is worth mentioning because a stand is incredibly useful for the wireless P-TTL-capable models which don't include it (the Pentax AF360FGZ and Metz 48 AF-1), and getting one separately is more pricey than it should be — see the section on generic accessories.
The Tumax DPT586AFZ includes a stand, but it's not a guarantee that all branded versions of this flash will; make sure to double-check.