.
Let preface my lists with a couple of conditions. Mostly what I would like to see of these is "more." By that I mean, in some cases there is opportunity to have another season or two, or some OVAs perhaps (examples: Otome Youkai Zakuro, NieA under 7). In other cases, a movie/OVA could have a sequel, or a prequel, or spawn a series (examples: Paprika, Strait Jacket).
Other cases, there is ample opportunity for a side-arc or three, by movie, OVAs or series (examples: Cowboy Bebop, Elfen Lied). I'm not limiting myself by available or announced manga material ... I'm interested in these titles because there are stories implied and suggested that could continue after the endings, or flesh out backstories of main or secondary characters to give the original story more depth.
In a couple of cases, I think the original was somewhat flawed and could be at least partially redone to lengthen the available anime and perhaps correct a few flaws along the way (examples: Utawarerumono, The Twelve Kingdoms). Along this line of thinking, there are some older titles that are hard to watch today because of the limitations of the animation industry at the time of their original release. Remaking some of these with modern animation technology, while still holding true to the original spirit and intentions of the story would be fantastic ... even re-working them to more closely follow the mangas & novels upon which they were based (example: 3x3 Eyes, Escaflowne, Eat-Man).
Catman, There She Is and Kung Fu Cooking Girls are pretty experimental shorts that could be expanded into larger projects, either as continuations or turned into a more feature-length version.
And, yes, some are out there with available material, which we expect to (hopefully!) generate more anime (examples: Twin Spica, NANA), whether or not it's already been announced (example: Index/Railgun).
These titles, to me, outlined and sketched worlds that are very rich for further exploration (example: Sora no Woto, Spice and Wolf, Mushishi) ... and, I would just like to see more from them, so long as the original standards are the minimum and that sequels, prequels, spin-offs, etc. would be at least to those standards.
These first two are somewhat special cases, so some explanation, and then I'll just list stuff and you can figure out from what I just said what would most likely apply to each title.

Lone Wolf and Cub. This needs to be adapted to as an anime series with hard-core adherence to the original manga. It is one of THE Epic samurai tales, and it's never been done right. This needs to happen.
Tenchi Muyo. The original OVAs and the original TV adaptation are really the only parts of this universe that I recognize. The rest of it went into a toilet of retardation and is just a horrible embarrassment. OKay, the movies not that horrible ... but it's a real shame that they just kept re-telling and changing the universe around. Going to the original, it would be nice to see that quality standard of humor and story told properly in a unified, definitive universe so we can forget the rest. Additionally, I'd love to see a prequel series that has no Tenchi in it at all ... needs a Space Pirate Ryoko series that tells (some of) the tales of Ryoko before she ever heard of Earth. Especially her notorious run-ins with Kiyone and the Galaxy police.
I could write up in detail for a lot of these titles, but To Hell With It. No time for me and I've probably bored you enough already. Yeah, I also
could add more titles, too ...
First list, titles not mentioned in this topic yet:
• REC • NieA under 7 • The Third • Texhnolyze • Paprika • Otome Youkai Zakuro • Omamori Himari • Ugly Yet Beautiful World • Yozakura Quartet • Twin Spica • Strait Jacket • Starship Operators • Dennou Coil • Girl Meets Girl • Ichiban Ushiro no Daimaou • Noein • Occult Academy • 3x3 Eyes • Level E • NOIR • Yokohama Kaidashi Kikou | • Miyori's Forest • Nausicaa • Read or Die • Serial Experiments Lain • Eat-Man • There She Is • Venus Wars • Yumekui Merry • Vampire Princess Miyu • Vexille • Yobi the Five Tailed Fox • Elfen Lied • Hen Zemi • House of Five Leaves • Kaichou wa Maid-sama • Kung Fu Cooking Girls • Planetes • Blue Submarine No-6 • Catman • Garden of Sinners • Lodoss Wars |
And, a
+1 to all of these:
• Toradora! • Angel Beats! • Cowboy Bebop • Hand Maid May • Irresponsible Captain Tylor • B Gata H Kei • Panty & Stocking w/ Garterbelt • Haruhi • To Aru Kagaku no Railgun • Index - only to flesh out the Railgun uiniverse • Working!! • Kiss x Sis • Utawarerumono • Ergo Proxy | • Time of Eve | Eve no Jikan • Nana • Skip Beat! • The Twelve Kingdoms • Trigun • Great Teacher Onizuka • High School of the Dead • Sora no Woto • Spice and Wolf • Durarara!! • Mushishi • Escaflowne • Samurai Champloo • Rurouni Kenshin |