Searching for books in a series?

As a fan of the fantasy/SF genre, one of the most annoying things used to be reading a great book set in an exciting new fantasy world, only to find it is volume two of a series, part one has already gone out of print, part three is difficult to find and needs to be ordered specially... and then discovering the author added another volume five years later which you didn't even hear about! The good news is ebooks and print-on-demand have taken care of disappearing series by keeping the earlier volumes available until readers have a chance to discover these new worlds.

Recently, I took advantage of this new technology to republish my out-of-print Echorium Trilogy and the Seven Fabulous Wonders series as ebooks, and now Amazon has made it even easier to find the missing parts of a beloved series by neatly listing the books together on one page of their site. If you're missing any of mine you can complete your collection here:

(I can't find a neat Amazon page yet for my Pendragon Legacy series, but when I do I'll add that here.)

Meanwhile, I am eager to complete my collection of a brilliant Anne McCaffrey series about sparky heroine Killashandra Ree, which began with The Crystal Singer - a book I first read years ago and often turn to when I need a comfort read, which means my battered old paperback copy is now falling apart at the seams...

Which much-loved series are YOU keen to complete?