Pinyin Combinations

JavaScript 1.6, 503 496 477 characters

function g(s){return/^([bfmpw]?o|[yjqx]ua?n|[ln]ve?|ei?|y[aio]ng|w?[ae]ng?|w?ai?|wei|y?ao|y?ou|y[ai]n?|yu?e|[^aeiou]+u)$/.test(s)|(((k=6*("ccsszzdflmnprtbghkjqx".indexOf(s[0])+(f=s[1]=='h')))|(r="a.e.ai.ei.ao.ou.an.ang.en.eng.ong.ua.uo.uai.ui.uan.uang.un.i.ia.ie.iao.iu.ian.iang.in.ing.iong.u.ue".split('.').indexOf(s.slice(f+1))))<0?0:k>84?r>17^k<108:parseInt("009m2f00b8jb009m2f00b7r3009m2n00b8jj1dwcfz0000rtfjba4f1xgbnjfj01rz1uyfb1009nn61b37cv1uyfa5".slice(k,k+6),36)>>r&1)}

Fomatted a little bit more readably (barring any errors in breaking the code into a few lines):

function _g(s)
{
  f = s[1] == 'h'
  k = "ccsszzdfghjklmnpqrtxb".indexOf(s[0]) * 6
  k += 6 * f
  return /^(weng|[bfmp]?o|[yjqx]ua?n|[ln]ve?|[ae]i?|y[aeiu]|y[aio]ng|[ae]ng?|wang?|wai?|we[in]|w[ou]|y?ao|y?ou?|y[ai]n|yue)$/.test(s) | 
         !!(k >= 0 && (1 << "a.e.ai.ei.ao.ou.an.ang.en.eng.ong.u.ua.uo.uai.ui.uan.uang.un.i.ia.ie.iao.iu.ian.iang.in.ing.iong.u.ue".split('.').indexOf(s.slice(f + 1)) & parseInt("00j85300mh2v00j85300mgan00j85b00mh332rsovz0002cp00b8jj00b8jjqmlts000b8jjv2mkfz3uwo3jv203jz3pwvelqmlts000jbaq2m6ewvqmlts03pwvdp".slice(k, k + 6), 36)))
}

The zero-initial cases plus a few one-offs are tested with a regular expression. After that, the table is encoded as a (concatenated) series of 6-digit, base-36 numbers, one per initial sound. The lookup then uses a pair of indexOf calls and a shift to select the right bit.

Tested against all cells in the table of combinations (filled cells tested for true, empty cells tested for false).

Edit: Replaced some of the 36 chars of the base-36 lookup with comparisons since g–, k–, h–, j–, q–, and z– have dense blocks of true/false.

Edit: Rearranged the bit test to avoid an unnecessary !! and compacted the regex more.