When I returned to fishkeeping after many years, I went slightly crazy and bought up a number of second hand tanks from Ebay, far cheaper than new. I actually bought 11, but one proved to have a leak, yet to be repaired, and one is set up as a British pond life tank, leaving me with 9 tropical tanks. Some of them came with a few fish included, but generally I was able to stock with whatever I wanted, limited mainly by the size of the tanks which are from 60 to 120 litres, i.e. not very big, but not nano either. All of the tanks were set up with soil under sand or gravel and heavily planted, then cycled and left for quite a long time before stocking. Like most people, I was fascinated by the sheer variety of fish available these days and was constantly changing my mind about what I was going to get. I soon realised, however, that I needed to be more realistic. I have moderately hard water and wanted fish that would be OK in it. I also added up prices and found that to stock with the more unusual fish would cost me a small fortune. Eventually I decided that the best option was to go for real “bread and butter” fish that would be cheap, hardy and get on with other fish without conflicts. As a result, I am now stocked entirely with small shoaling fish. I'm very happy with the results, particularly when I read about the health and other problems reported by people on this forum. I like all of my fish (30 types) but I've selected 10 which I would thoroughly recommend for anybody who wants easy care, hardy, cheap, small shoaling fish, tolerant of a wide range of water conditions, which would be particularly suitable for the beginner. Mine are all in shoals of 8 to 12 and they do need to be in shoals to loom their best.
Zebra danio. Although some people reckon these need a large tank, I've found that my shoal of 10 are perfectly happy in 80 cms. They zoom round and round, up and down, in and out of the plants, constantly on the go. Very common for good reasons, bomb-proof, lively and attractive.
White Cloud Mountain Minnow. All of the virtues of the Zebra, not quite so manically active. Both these can be kept at lower temperatures which can help with running costs. If these were rare, people would pay a lot for them.
Harlequin Rasbora. These always look delicate, but in fact seem to be remarkably tough. Apart from their two close relatives, they have a look which is quite different from anything else. Mine are always very laid back and don't seem to be bothered by anything.
There are many species of barb, but a lot of these grow quite large. I have Ruby and Green Tiger which are great fish but very boisterous and therefore perhaps not ideal for all communities. I've picked out two smaller and peaceful barbs, but others such as Checkered and Five Band would be equally suitable.
Cherry barb. Much smaller than most and generally very quiet, but not shy. While the males do have the brightest colours, the females are also very attractive with their contrasting red fins.
Odessa barb. Very unusual colour, with the red band running along the body, active and lively. Doesn't grow big and can be kept in a cooler tank.
There are many species of tetra which would be suitable but some do need softer more acid water, while the popular Neon appears to have some health problems, though mine are all fine.
Glowlight tetra. Appears to have lost popularity, but still a great fish with its glowing red body stripe and a very undemanding species.
My other two tetra choices are perhaps rather neglected, probably because in the LFS they just look like little colourless silvery fish. When settled in they become very attractive in an understated way.
Silver tip tetra. Very lively, the males more colourful than the females, the tips of the fins and tail really stand out. Very hardy and said to have a life span of 7 years, they are 6 for £5 at my LFS, what a bargain!
Lemon tetra. Very much a fish which needs to settle in to look its best, but a shoal has an elegance that is difficult to describe without seeing, not a gaudy fish but one with poise.
My last two do tend to be more expensive than those above, but are definitely worth it.
Celestial Pearl Danio. Most “nano” fish seem to require soft water, but these thrive in my moderately hard water. Tough little characters, mine arrived (mail order) at not much more than 1 cm long, but on a diet almost entirely of powdered dry food they have thrived, grown, developed their full colours and bred. You do need to get close up to appreciate their remarkable colours, but that's a good excuse to sit with your face a foot away from the front of the tank staring into it.
Panda corydoras. There are many species of cory, but some grow quite large, while the smallest can require very close viewing to appreciate. Pandas are the happy medium, small enough to fit a shoal into a smallish tank, but big enough to be seen easily. They also have an attractive pattern and seem to be considerably livelier and more active than some of the larger species. Full of character.
So those are my choices, I'm sure others will have different ideas. However, I would suggest that most beginners might find things a lot easier if they chose fish like these, rather than going for the oddballs or those that “looked nice in the shop”, surely the worst way to choose fish.