Jolan'tru, rhadai galaen s'Tal'Diann.
There are several sites about the Rihan language, including our own Catoena Rihan vr'Doaegevha u'Klhuedhevha (Romulan Language and Culture Institute, or RLCI), still being built, and which includes an interactive (searchable) Romulan-to-English/English-to-Romulan Dictionary. Our site is based largely on the work of the next two sites I will give, but is also building upon them, taking vocabulary from the final version of the first of those two which was never added to the dictionary in that site (and thus also failed to make it into the second of the two), and adding additional terms which we have had to create by compounding other words from the pre-existing vocabulary in order to supply Rihan versions of terms used in Star Trek Online (such as "Kreh'dhhokh" for "Republic," derived from "kreh" ["thing"] + "dhhokh" ["common," one of the words used in the final version of CIRL, but never added to the lexicon thereof, and therefore also never added to IRLI], and thus essentially a literal translation into Rihan of the Latin word "respublica," meaning "public thing" or "public concern," a compound of two words in Latin, "res" ["thing," with all the vagueness of the English word "thing"] + "publica" ["public"]; the Latin word "respublica" is the source of the English word "republic"). Most of these newer vocabulary items have yet to be added to our own RLCI dictionary, but "coming soon." We have also taken material from sites which have been gone from the internet for quite some time and are now available only at the Internet Archive's Wayback Machine. CIRL has also had a spotty history, at times being available only via the Internet Archive's Wayback Machine (I give the link to the most recent update from there, rather than the current version at its own URL, which has lost some of the newer content, both because of the newer content still being at the Internet Archive and because the actual site has been unstable; the reason or reasons for the instability have been explained in more than one way, and I'm not sure which is accurate).
Of the other sites, the two best-researched (and best-developed) are:
Partair Doaege Rihanai (which I generally abbreviate as "CIRL" for "Central Institute of the Romulan Language," as the group responsible for it named itself)
Catoena ih'Shiar vr'Doægevha Rihanh'ri (which most people generally abbreviate as "IRLI" for "Imperial Romulan Language Institute," the name taken by the group responsible for it)
These two offer significantly more than simple wordlists, have been meticulously researched, and are the most internally consistent.
The second is built upon the first, but I like the organization of the first better. The second, though, has lessons, which the first does not. However, there was a project going on to update the first at a new URL address, which apparently never finished. The Internet Archive's Wayback Machine has preserved an archive of the update project, which has some nice features not found in the original, like this alphabet, and a page of links to various literary works (or parts of works) which have been translated into Rihan (which contain some additional vocabulary not found in the dictionaries of the second and third links I gave above).
There's also a searchable dictionary available here (although the vocabulary does not reflect additional terms which aren't included in the last three links I gave above, such as are found in the update project's literature section):
This one offers a bit more than a wordlist, but, when compared with the previous two, leaves a bit to be desired:
In addition are the following (after the first of these, which provides some info on Romulan alphabets, the rest are in no particular order), most of which consist of little or nothing more than lists of words (and occasional phrases):
Romulan alphabet and the Rihannsu language -- It should be noted that the "Useful Phrases" on this page are weak, due to inaccuracy and a failure to make use of the grammatical rules of the Rihan language. However, I'm working on correcting these for inclusion in my own miniature phrasebook (linked near the bottom of this page).
ENGLISH - RIHANNSU DICTIONARY V. 3.1
Romulan - English dictionary
(note that this site also has links to download two Romulan fonts)
Romulan language - Memory Beta, non-canon Star Trek Wiki
And then there's my own miniature (but still growing) phrasebook, found here (in which I give Standard Rihan, but I am also developing for that phrasebook a dialect of Standard Rihan in use on one of the colony worlds, which so far differs from Standard Rihan only very slightly, and only in accent, or more precisely, in phonology/orthography):
Rhirhalir Rhudheriin Raeler (Often-Used Phrases)
Last, but by no means least, a Google+ Community to promote discussion and study of the Romulan language:
Romulan Language and Culture Institute Google Plus Group
G'essatra ir'Virinat t'Prell,
galae'Enriov s'Tal'Diann ch'Mol'Rihan,
Orrhanen u'hru'Phi'Tlarum Mol'Rihanai,
ri'irrah Eirethai Nodaire'enhai (hru'i'Ernrahhedhai) Catoenam Rihanai vr'Doaegevha u'Klhuedhevha
|Flaihh'u ch'Rihan! Flaihh'u ch'Virinat!|
(Last Update: 2014-06-14-pm)