I just read the first volume of Akira (found a weird hard cover edition dirt cheap), and I loved it. I've always been kinda ambivalent towards the film. There's just so much crap happening at breakneck speeds, and most of it doesn't make a whole lot of sense when you scrutinize it. Every time I watched it, I ended up being more confused. Anyway, the manga seems to have a much improved pace, and seems to be heading toward some much needed exposition on just what the fuck is happening.
If the ambiguity of the ending was what annoyed you about the film, you'll definitely enjoy the manga more. The end of the film is only the halfway point of the manga.
Blade of the Immortal starts out strong, but fades into mediocrity after a while. About 70 issues in it becomes obvious that Samura is just milking the story for as long as it remains popular. I bought Dark Horse's single issues right into the 100s when it seemed to be building to a climax. Instead the critical confrontation was awkwardly sidestepped and the story started trundling back on its road to nowhere. I was so sickened by that point that I cancelled my subscription and sold my collection except for the first few story arcs.
I highly recommend most of Osamu Tezuka's works. Only two volumes of Black Jack have been translated, but they're great. Adolf is top notch. Phoenix and Buddha transcend manga's present day commercialism to become truly moving works of literature. If you don't want to spend a lot on a whole stack of book, then just get Phoenix volume 4: Karma (each volume stands alone); I rank that one alongside the great works of any writer.
I don't think it's been reprinted in recent years, but track down the nine volume Sanctuary series if you can. It's a mature and complex drama where the world of politics mixes with the underworld of the yakuza. Its only flaw is a slightly rushed ending.
Junji Ito's three volume Uzumaki is easily the best horror manga available in English. Forget the mediocre movie version; the original manga is one of the most original, disturbing and memorable horror concepts in any medium. If you like that then try the two volume Gyo manga. Not quite as great, but still good.
Maison Ikkoku is a long-standing favourite of mine. It has all the quality of Rumiko Takahashi's more commercial stories, but with a more mature tone and a story that actually goes somewhere instead of rolling around in circles.