I'm currently eliminating both of my 30" tanks. I will never set one up again for anything other than just plain fish.
A 2x55w PC fixture will get the job done for a 29g, but your coverage will be less than perfect, and that's the biggest issue for us. You really should consider another footprint for a plant tank.....I like the 10g, 20h, 40breeder. You can do a 40 breeder for very nearly the same price as a 29g....Especially if you build your own stand.
If you're stuck on the 29 (that's cool!), then you have some options:
If this is your first plant tank, I *strongly* suggest that you use normal output flourescents. There are are a few ways to get adequate light.
You could get a twin 20w strip and a single 20w strip which will give you enough light to grow *nearly* anything. Depending on how handy you are, you could build your own hood and fit as many as 4 NO (normal output) bulbs into it. There are several commercialy available electronic ballasts that wil make your life easier in this arena. If you're interested, just ask!
Power compacts are now very trendy to use on plant tanks, but are quite powerfull, efficient, and easy to work with. They can be had quite cheaply as a kit from www.ahsupply.com
Just keep in mind that, with all this power comes another set of problems. With this quantity and quality of light you're much more likely to "crash and burn" with regards to algae, fertlizer prolems and CO2 requirements just to scratch the surface, than with a more modest set-up. I suggest that if you do go this route, that you be very carefull, test often, and ask alot of questions.
You could also use a twin VHO (very high output) set-up that will give you more light than a PC set-up, be as easy to install, but cost you more. Reefers like these alot, but they seem to have gone out of style for us plant guys.
Stay away from expensive, pre-assembled, power compact fixtures like the Coralife Smartlites, Helios PC's, and those crappy All-Glass PC fixtures. They have lousy reflectors and cost as much or way more than the AHS kits for much less product. Unless you REALLY don't like putting stuff together, try to build your own stuff. It cuts down on empty wallet syndrome.
Also, be very wary of advice given from pet store people about plant stuff. Ever hear the saying "A little knowledge is a dangerous thing"? That's been my experience with LFS workers *most* of the time.
50/50 bulbs are worthless for a plant tank, BTW.
Hope this helps!!