Yes, although most of the apps that print directly from iOS to a networked printer (i.e. a standalone printer with an embedded printserver or one coupled with an external printerserver device) will come pre-packaged with drivers that only support a specific gamut of printers. This is out of necessity since the iPad will have to know how to talk to your printer without the benefit of your computer.
Three apps I'm aware of (and undoubtedly there are more, but these are the three I've researched) are: Print Central, Print Magic and ePrint. Print Magic also has a free 'lite' version that you can use to test if your printer is compatible.
Besides having to check if your printer is compatible, you'll also need to have a good grasp of how your printer is designed to function over a network. Some of the apps will look for Bonjour-supported printers and do much of the setup automatically. Others will have to be set up manually, which can be a non-trivial affair if you're unfamiliar with networking basics.
Another caveat to be aware of is that as far as I know, none of these apps support AirPrint directly. In other words, you won't be able to use the builtin 'Print' function in apps such as Pages, for example. You must do all your printing from within the printing app itself, which means you'll have to import your material to be printed into them first. (I could be wrong about this, but most of the direct printing apps I looked at worked this way).
If none of this has scared you off, then I can at least report my success story: I was able to get my iPad printing directly to an old HP LaserJet 6MP + HawkingTech printserver using the ePrint. In order to do this I had to use LPR/LPD style printing and manually specify the printerserver address and queue name. It prints things a lot slower than my desktop, but in all honestly, this is the first app I was able to get working so I have no baseline for comparison.
Hope this info helps, somewhat.
