My set of open-end/box-end metric wrenches are probably the most used items, closely followed by my metric socket set. For most DIY stuff, you're not likely to need anything larger than a 19mm or so. Also a small assortment of screwdrivers, allen wrences and allen-head sockets, needle-nose pliers, a couple of sizes of vise-grips, one of those multi-tool thingys for electrical cutting/stripping/crimping, a few mid-sized deep sockets (for glow plugs/spark plugs/hard to reach stuff/etc.), and a nice hammer to smash things with when all else fails!--Just kidding!
For a DIYer, I don't see any reason to spend tons of money on anything other than Craftsman...They may not be the ABSOLUTE best tools, and you may break one or two someday, but they have a lifetime warranty, so who cares? Go get another one for free.