It struck me earlier that the word précis is an interesting one. The s is silent in the singular,so I would say "I wrote a précis" (pronounced pray-see), but in the plural, despite the fact that the spelling is the same, the s is pronounced as a z: "I wrote several précis" (pronounced pray-seez). Précis entered English from French in the 17th century, and we have kept the French pronunciation in the singular, but not in the plural -- presumably because we are more comfortable with plurals that end in -s. When we put verb endings on précis, the s remains silent: précised (pronounced pray-seed) and précising (pronounced pray-seeing). Rendezvous behaves exactly the same way; we only hear the s when we are talking about rendezvous in the plural. Rendezvous entered English from French in the late 16th century, although at that time it had a military sense. I don't often talk about a number of chassis, but I imagine that this word would behave the same way (silent s in singular and z sound in plural) as it also comes from the French.
The majority of singular nouns in English that end in -s end in -ss, and particularly -ness eg class, business. Their plurals are regular ie -es is added: classes, businesses. There is a group of nouns that end in -is eg thesis,analysis, crisis whose plural ends in -es (theses, analyses, crises). Note that axes is pronounced axe-eez, when it is the plural of axis (it's pronounced axe-ezz when it's the plural of axe) and bases is pronounced base-eez when the plural of basis is meant (bases is pronounced base-ezz when it's the plural of base). There are quite a few nouns that end -us eg syllabus, cactus, virus, and these have plurals ending either -i (cacti) or -uses (viruses). Corpus is irregular; its plural is corpora.
There is also a small group of nouns ending in -is which add -es to form the plural eg iris - irises, trellis - trellises, portcullis - portcullises. I've never needed to talk about more than one pelvis, I don't think, but the Oxford Dictionary of English tells me that the plural can be pelvises or pelves (pronounced pelv-eez, of course).
The words aerobics, phonetics, billiards, measles, shambles, gubbins etc are treated as singular nouns, but they began as plurals (a lot of words ending -ics are like this). Once all these groups are discounted, and three-letter nouns ending in -s, like bus and gas, are also excluded, there are very few singular nouns in English that end in -s. Here are the ones I can think of: bias, alias, atlas, canvas, pancreas, series, species, jackanapes, maths (but this is from the -ics group mentioned above), lens, chaos, rhinoceros, corps (from French, plural the same), mews (this was originally the plural of mew) and news. Rickets can be singular or plural, and bossyboots obviously ends in an -s because the person is wearing two boots. Biceps, triceps and quadriceps are both singular and plural; they're each one muscle, but divided into two, three or four different sections.