Recently, Subversion 1.5 has been released, and alongside with it the excellent Windows client TortoiseSVN. SVN 1.5 adds basic support for merge tracking, which is a very nice feature which is especially important if development is mostly done on branches.
TortoiseSVN 1.5 brings full support for all of SVN 1.5 (including merge tracking visualisation) and fixes many Vista related bugs. One small problem remains, if you had previously "Enable accelerators on top-level menus" enabled to get properly drawn context menus, you'll notice that no icons are drawn in Vista now. Easy fix: Delete the registry key
HKCU\Software\TortoiseSVN\OwnerdrawnMenus -- works like a charm afterwards.
Windows binaries for SVN 1.5 itself should appear during the next week.
[Update] Updated registry key, thanks to Markus for pointing this out.