There's really a lot of options. It all depends on what it is you are looking to do. I really like the Ashley Outdoor Big Dot tritium sights. Its a big fat white dot that really shows up fast and easy for CQB type shooting. Plus the big white dot shows up WAAAAY easier in that time between light and dark when it is too dark to see the front sight well, but not dark enough for the tritium to start glowing. The downside to this system is that it is big and well make accuracy a little harger out at extended ranges.
Another option is the Trijicons. Most people, myself included, dont feel the rear tritium sights are necessary. Just go with the front. The rear sights are too close to your eye to really do anything at all in my opinion, and are a waste of money... YMMV.
These front sights are VERY easy to install. However, the front sight adjustment tool you can buy most places sometimes dont work with these tritium sights because of the way they are designed.