The music of Orlando di Lasso--or Orlandus Lassus, or Orlande de Lassus, Orlande de Lattre, or Roland de Lassus, or Roland de Lattre, take your pick!, hasn't been overlooked in recent years. On the contrary, there have been a large number of new releases (at least, for a Renaissance master). Most fortunately, the pre-internet days of my being forced to visit 'used' record shops for years!, in search of a rare out of print LP or CD of the Hilliard Ensemble's recording of the Penitential Psalms, so that I might be able to finally hear this music for the first time, are long gone.
Yet, Lassus remains one of the most prolific, versatile, and linguistically diverse composers in music history, composing over 2000 works, in 5 different languages--Latin motets & masses and other liturgical works, Italian madrigals, French chansons, German lieder, and Dutch songs (though none of his Dutch songs have survived). (As far as we know, Lassus composed no instrumental music.) Hence, there are a great many Lassus works that have never been performed since his time, or recorded in modern times. Nor can I recall any comprehensive box set of his music either (except for the 5 volume series on Musique de Wallonie that GioCar mentions, which hasn't been boxed, and what may be an ongoing Lassus series from the group Die Singphoniker?). I expect the 'mother' of all box sets will one day be released, should Lassus' opus ever become more extensively recorded. So, at present, you have to create your own box set. The good news is that there's lots to choose from (& I've placed an asterisk next to my special favorites):
At the top of my list, I'd strongly second Mandryka's recommendations of the Hilliard Ensemble and Henry's Eight--(1) especially their two recordings of Lassus' towering masterpiece, the seven *Penitential Psalms, or Psalmi Davidis poenitentiales. Both recordings are essential in my view, since the Hilliards add instrumentation (performed by the Kees Boeke Consort), while Henry's Eight employs only voices--a small choir of eight singers. I wouldn't want to be without either recording, since these motets are widely considered to be among the greatest works of the Renaissance, and deservedly so, in my view.
There are also two good chamber choir versions from Collegium Vocal Gent, led by Philippe Herrweghe, and the Kammerorchester Josquin Desprez. But, as noted, I'd choose the Hilliards and Henry's Eight myself, since I prefer only one or two singers on a part in Renaissance music. For me, it's especially important to hear the polyphony clearly, and for the singing to be lithe and nimble.
(2) I find it more difficult to recommend a first or second choice for Lassus' final somber masterpiece, his swan song: a set of 21 madrigali spirituali entitled, the *Lagrime di San Pietro, or "Tears of St. Peter". The decision probably lies between the following good to very good recordings:
(this recording differs from the below recordings in that Picotti chooses to add subtle instrumental accompaniment to his vocal ensemble, Capella Ducale Venetia. Btw, this group has also made a fine recording of Andrea Gabrieli's Psalmi Davidici:https://www.amazon.com/Andrea-Gabri...529262210&sr=1-1&keywords=picotti+capella+cpo
Although I've not heard the recordings by Ars Nova, led by Bo Holton (on Naxos) or the Chamber Choir of the Liszt Ferrenc Academy of Music, led by István Párkai. With that said, I didn't like Hofkapelle in this music, nor was I entirely crazy about the Dufay Ensemble's recording, either.
Beyond those two essential Lassus masterworks, I'd recommend considering and sampling from the following recordings:
(3) Motets and other sacred music--masses, hymns, canticles, Magnificats, responsories for Holy Week, Passions, Lamentations:
Prophetic texts, or Oracula:
--*Prophetiae Sibyllarium--12 motets (my first choice is *De Labyrintho's recording; second choice, Ensemble Daedalus, & third choice, Cantus Cöln. I've not heard the more recent Brabant Ensemble recording.):
--Lectiones Sacrae Novem ex libris Hiob (9 texts from the Biblical book of Job): To my knowledge, *Ensemble Daedalus is the only ensemble to record this work (it comes coupled with their "Prophetiae Sibyllarum"):
--*Lamentatio Jeremiae Prophetae, or Lamentations of Jeremiah (By default, my first choice is Ensemble Vocal Européen, led by Philippe Herreweghe; second choice, Ensemble Officium, and third choice, the Huelgas Ensemble--but, as mentioned, I prefer one or two singers to a part over these large choirs):
Works of Marian devotion:
--Salve Regina, Ave Maria, Salve Regina mater, Ave Regina coelorum, Missa est angelus, Regina coeli laetare, Santa Maria, etc.--performed by the *Orlando di Lasso Ensemble, Hannover (a fine group): https://www.amazon.com/Mariengesang...=1-3&keywords=orlando+lasso+ensemble+hannover
--Stabat Mater: Hilliard Ensemble:
--Requiem (first choice, Hilliard Ensemble, second choice, Pro Cantione Antiqua of London, led by Mark Brown):
--Missa super Dixit Joseph (& motets): *Cinquecento: https://www.amazon.com/Lassus-Missa...d=1529225259&sr=1-4-fkmr0&keywords=lassus+CPO
--Missa "Tous les regretz"--Huelgas Ensemble, dir. Paul Van Nevel: https://www.amazon.com/Quinta-Essen...529262404&sr=1-1&keywords=paul+huelgas+lassus
--Missa super "Osculetur me"--the only recording I know of this important double mass is by the Tallis Scholars, but unfortunately, Peter Phillips has transposed the mass up, & I don't think it works especially well in this case:
--Motet: *"In monte oliveti"--the Hilliard ensemble & *Singur Pur (on Musique de Wallonie) are excellent:
(The Hilliard recording is from their CD: Lassus Motets & Chansons, and includes the Stabat Mater:
--Canticum Canticorum (sacred motets):
--Hymns: Die Singphoniker: https://www.amazon.com/Hymns-Die-Si...-1-fkmr0&keywords=Die+Singphoniker+lassus+cpo
--Magnificats: Die Singphoniker: a single CD selection--Lassus composed around a hundred Magnificats, so I hope this group will keep going: https://www.amazon.com/Magnificat-D...-2-fkmr0&keywords=Die+Singphoniker+lassus+cpo
--St. Matthew Passion: Paul Hillier, Theater of Voices (though I've not heard the more recent Naxos recording by Musica Ficta, led by Bo Holton): https://www.amazon.com/Lassus-Matth...575&sr=1-2&keywords=lassus+st+matthew+passion
--Cantiones Sacrae sex vocum--Collegium Vocale Gent: https://www.amazon.com/Cantiones-Sa...TF8&qid=1529261849&sr=1-36&keywords=de+lassus
--Magnum Opus Musicum (a collection of 516 Latin motets & secular works, which were published posthumously by Lassus' sons): *La Fenice, led by Jean Tubéry, is excellent in a selection of music from this collection:
4) Secular music--Italian madrigali, French chansons, German lieder, etc.. I would most recommend Lassus' madrigal cycles set to poems by Petrarch, especially the recording by the *Orlando di Lasso Ensemble, Hannover, which is a favorite of mine:
--German lieder (French chansons, & Italian madrigals):
Capilla Flamenca, led by the late Dirk Snellings--another very fine group (also see the Die Singphoniker release above, as they've recorded 8 French chansons):
Ensemble Clément Janequin, led by Dominique Visse: https://www.amazon.com/Lassus-Ensem...9346832&sr=8-7&keywords=lassus+harmonia+mundi
--Villanelle, moresche, canzoni, chansons, madrigali: Concerto Italiano:
6.) I've not heard the following recordings:
7.) There's also an excellent 'biographical' Lassus series on Musique de Wallonie (presenting his music according to the different stages of his career), which has already been mentioned (Volume 5 is the last volume in the series, so it is complete):
That about covers it.