Although a large portion of early open reel models were transportable, those are listed in Vintage transportable R2R's section since these were actually the norm rather than the exception well into the 60ís. Here we list truly portable recorders of the 50's and 60's including the small transistorised and hybrid mini recorders that started to appeared in the late 50's, these were truly portable and capable of running on battery power but were something less than hi-fi, the small spool sizes meant that the tape had to be run slowly to archive a reasonable running time and to keep costs down the mechanisms were often simple. However this format gained popularity with travelling salesmen and executives since the format was more universal than the Dictation Belts and similar voice recording technologies and are surprisingly common on the second hand market considering that they mostly disappeared in the early 70's.
Bang & Olufsen As far as I can gather the first portable open reels from Bang & Olufsen were the Belcanto and the Beocord Stereo Master, both introduced in 1962 and manufactured into 1964, the Beocord was replaced by a portable version of the Beocord 2000 referred to as K+, shared the same specifications as the other 2000 models and was manufactured well into the early 70's. Strangely enough the Belcanto is the one that most often pops up for sale despite the short production run. You can find pictures of all the portables on this French B & O Fan site.
Craig American company but sold Japanese made miniature recorders in the 60's, some models are apparently Aiwa and JVC but most later models appear to be manufactured by Sanyo and Pioneer, also note that the number on the identification plate on these model are often different from the model numbers from the company in keeping with their OEM origins. The 212 is by far the most common model, powered by 6 C size batteries or a 9v transformer, accommodates 3" reels and has 2 speeds, is a budget mono model with auto leveling and is intended for voice recording and included a microphone with a start/stop function, the identification plate names this model as the 2102. Later 401 model is much smaller ("spy" type) and powered by 4 AA batteries. The company also owned the Vista brand and under that name produced the Tapemaster series of portable recorders in the late 50's (those were unusually small at the time) and later models similar to the Graig lineup.
Fi-Cord Portable recorders, the best known is the 202 model that was built for them by Erskine in the UK in 1959 and produced until 1962 at the least, these were considered to be something of a marvel at the time due to their small size and some semi-professional qualities, you can get a data sheet for that model here. But my favourite model has to bee the 1A a miniature recorder built for Fi-Cord by the company that later became Stellavox and is the predecessor to the Stellavox Sm5, this is one of the earliest transistorised recorders (8 transistors as the ad proudly proclaims) and has a respectable audio specification not better than most quality home recorders of the day. All post 1963 models from the company such as the E-222559 (usually called 222 I believe) seem to have been made in Switzerland, do not know if they were all built by Stellavox.
Geloso While all of their earlier consumer models appear to have been transportable the only truly portable model I have seen is the mid 60's G 70, it's a mono model intended fo voice recording and nowhere as common as the older machines from the company.
Hornyphon All portable models featuring this name seen to date have been rebadged Philips units, some having the same model designation but some of the 50's early 60's models have different ones. This factory also made the professional lineup of Philips recorders in the 1960's.
Sears Most Sears tape recorders were actually sold as Silvertone but one portable model the 8230 was sold labelled as Sears and is one of the more common units out there. It's of Japanese manufacture and it's should be noted that while it's a portable model it's designed for AC operation only and that the unit came originally with a tabletop mic, a headphone adaptor and a speaker adapter (with alligators). The unit has inputs for a microphone and radio, a speaker output and a small built in monitoring speaker, one unusual feature is that it appears to be able to take slightly bigger spools than other recorders of a similar size, age and application (Cine reels probably) also the speeds are 9,5 and 15cm wich is higher than on most such portables. Early models from the mid 60's or so (?) were a sort of light beige in colour with a light brown control panel but later models from ca 68 were white with a black or dark brown control panel. Weight is approx. 9kg.
Studer The company really only made 1 truly portable product, the mono Studer B30 that was introduced in 1957 and manufactured into the 60's.
Tesla Made loads of portable models in the 60's and 70's including the Uran that was introduced in 1966, a versatile recorder that could be run from batteries, AC or DV12v. The Uran was a replacement for the B54, and early 60's models include the B46 and B41. they also manufactured the B4 model at the same time but that was really intended for voice recording rather than music recording as can be seen by the speeds it offered, 2,38cm (15/16ips), 4,75cm (1 7/8ips) and 9,5cm (3 3/4ips).
Trix A company that makes model trains and similar stuff, in the 50's and early 60's it made a range of portable tape recorders including the miniature 88 (some variations marked Phono Trix 88 other just Trix 88), that was one of the earliest micro open reel recorders and was extremely well built despite appearances, that majority of the units that I have seen were fully functional despite being 40 years old or so is a testament to this. Some of their earlier models were also called Phonotrix and were remarkably small for their time but hardly miniature. The Trix Express page has info on their portable models but in German only at the moment.