If you enjoyed the ingenuity and the detective aspect of the Holmes canon, I would strongly recommend two other classic mystery authors who also created real literature, Dorothy L. Sayers and Rex Stout, one British, one American.

In case you have ever seen TV adaptations of Lord Peter Wimsey and Nero Wolfe (one is currently running on the Discovery Channel, and it's not a very good adaptation of Rex Stout -- makes both Wolfe and Archie into buffoons), don't let them put you off. Likewise the Ian Carmichael portrayal of Lord Peter which the BBC did, poorly.