As Nettie says, primes are the best option. The manufacturers have to make compromises opticaly to get zooms to work at all focal lengths, but modern zooms are very good.
Another option for lenses is the old M42 mount manual focus primes with an EOS adaptor. All the shots in my link above were shot on 1950's, 60's and 70's glass. With careful purchasing, you can get 5 or 6 mint condition lenses for the same outlay as one decent modern lens.
Obviously they aren't as convenient for terrestrial work being manual focus, but many of them are as sharp as, if not sharper, than what is available today with the exception of $1000+ glass like Canon's L series.
Some of them are still considered excellent lenses today.
Stick to the better known brands like Nikkor, Leica, Carl Zeiss, Contax etc, though there are a few examples of one type of lens that goes by many generic brand names that have a cult following (like the 55mm f1.2 Revuenon/Rokinon/Yashinon/Chinon etc etc, all the same lens, made by Tomioka)
Check out the Manual Focus lens forums
Here and
Here to get an idea of what is good.
Sadly though, due to the increased popularity of these lenses since the advent of DSLR's and now the the Sony NEX's, demand and therefore prices have jumped considerably, but good clean examples can still be had for a good price on Ebay. Ignore all the way overpriced 'Buy It Now' examples, they are sellers preying on the inexperienced.