JetBrains, now the editor of famous IntelliJ IDEA, presents AppCode, an Objective-C editor that manages MacOSX and iOS targets. It requires XCode (notably to edit Nib archives through Interface Builder, now part of XCode since version 4) and uses Google Protocols Buffers technology to launch iOS Simulator (as it isn’t available on Windows, AppCode can’t be cross-platform). Among first reviews (see here and there) some problems are reported with files/imports, however auto-completion seems more powerful than the one in XCode, and the interface looks closer to Eclipse one (and simplier than XCode one), despite being less Cocoa compliant then (see AppCode UI overview).
As for IDEA the solution isn’t free (131 euros for a commercial license, 61 euros for a personal license), however its quality and support level, and its lite interface that allows faster acceptance for developers used to Eclipse, may be interesting. A mac will always be required however. A demo version (30 days trial) is available.