not in any particular order and i'm assuming you mean haute couture or higher-end clothing/accessory designers:
armani, bcbg max azria, alexandre de paris, alber elbaz, mary quant, loris azzaro, maxmara, cerrutti, valentino, dior, junko shimada, dries van noten, gucci, nina ricci, karl lagerfeld, galliano, marc jacobs, madame gres, ermenegildo zegna, trussardi, imitation of christ, custo barcelona, chado ralph rucci, badgley mischka, stella mccartney, etro, oscar de la renta, bill blass, bob mackey, miuccia prada, miu miu (i suspect that prada is behind this) missoni, alexander mcqueen, loewe, vivienne westwood, ann demeulemeester, jil sander, giambattista valli, versace, krizia, kenzo, ghost, iceberg, byblos, issey miyake, yohji yamamoto, commes des garcons, junya watanabe, arnold scaasi, geoffrey beene, donna karan, calvin klein, zac posen, proenza schouler, narciso rodriguez, tom ford, loro piana, chanel, givenchy, judith leiber, ralph lauren, marchesa, carmen marc valvo, malo, st. john, escada, sonia rykiel, jacques fath, balenciaga, pucci, schiaparelli, hussein chalayan, gaultier, richard chai, cynthia rowley, pierre balmain, pierre cardin, lanvin, hermes, burberry's, zandra rhodes, anna sui, gianfranco ferre, scherrer, lacroix, rocco barocco, paco rabanne, romeo gigli, maud frizon, andre courreges, abu jani, sandeep khosla, cavalli, carolina herrera, rathore, fendi, ferragamo, anna molinari, yves saint-laurent, alberta ferretti, emmanuel ungaro, oleg cassini, derek lam, nanette lepore, norma kamali, isaac mizrahi, kate spade, la perla, nicole miller, vera wang, collette dinnigan, les copains, olivier theyskens, martin margiela, luella bartley, temperley, hemant trivedi, diane von furstenberg, matthew williamson, mulberry, viktor&rolf, azzedine alaia, louis feraud, nicolas ghesquiere, tocca, claude montana, jean patou, hedi slimane, helmut lang, elie saab, monique lhuillier, rifat ozbeck, manish malhotra, anand jon, lulu guinness, hanae mori, dolce gabbana, roberto capucci, giorgio sant'angelo, angnes b., enrico coveri, trina turk, herve leger, john varvatos, mary mcfadden, francesco smalto, koos van den akker, per spook, angelo tarlazzi, gerard pipart, regina schrecker, fernando sanchez, tan guidicelli, scott crolla, joan vass, louis vuitton, caroline charles, jaques azagury, wim hemmink, michael kors, thierry mugler, guy laroche, perry ellis, carlo tivoli, pino lancetti, dik brandsma, eric mortensen, dominique morlotti, marc bohan, frederic castet, jaques heim, dsquared^2, tarun tahiliani, satya paul, shelli segal, christian louboutin, jimmy choo, manolo blahnik, giuseppe zanotti, randolph duke, lacoste, david meister, zang toi, blumarine, marni, akris, anne klein, dana buchman, eileen fisher, betsey johnson, adrienne vittadini, elie tahari, lilly pulitzer, tory burch, christina perrin, halston, piazza sempione, ellen tracy, juicy couture, moschino, tufi duek, behnaz sarafpour, catherine malandrino, yigal azrouel, delman, bruno magli, paul smith, 7 for all mankind, doo ri, rodarte, thakoon, bottega veneta, mayle, veronique branquinho, luca luca, rochas, sisley, celine, alice roi, joseph abboud, bradley bayou, julie chaiken, louis dell'olio, victor costa, sean combs, kenneth cole, g. mendel, gemma kahng, colette malouf, sigrid olsen, mary jane marcasiano, tracy reese, judith ripka, christian roth, peter som, cynthia steffe, jill stuart, vivienne tam, patricia underwood, stuart weitzman.
liz claiborne, vera bradley, ann taylor, etc. are designers too, but i didn't know if you were including more mainstream designers like them as well.
ok, i've named all the ones i heard of. i know i've missed many that i have heard of, but this is what i came up with. hopefully i've named more than you!!