Rhiannon Shaw's Aidan Series is pretty epic, especially Sirocco (http://rhi.moonlit-eyrie.com) -- and I don't say that just because I betaed parts of it. It's pretty huge, size-wise, and covers a lot of ground.
I have a sense that the LJ format lends itself to shorter fics. The longer stuff is getting posted elsewhere, in other fandoms -- SGA has Speranza's "Written by the Victors", for example -- and anything more active than HL is currently is likely to have the longer story because people are feeding the need. That isn't to say someone isn't writing long stuff; I wrote "Falling to Pieces" last year, and it clocks in at 254 KB.