The Jurys chain is the way to go- they have several hotels all over the city. I stayed in July at their newest one at Parnell Square for €79 a night. The Jury's at Christchurch Cathedral is the closest to Temple Bar, where most of the loud pubs are. They do tend to get a lot of tour groups there so they can be busy, but they are good value. There are several other smaller, cheaper places to stay (mostly north of the Liffey on Gardiner St, near the big bus station) but that neighborhood is not so great. Check out www.jurys.com
and it will show the prices for all their hotels at once.
If you're looking to spend a little more, I highly recommend the Brooks Hotel. Very central location and their new renovations are great- plasma TVs and a TV mounted into the tiles in the bathtub. Plus they have speakers in the ceiling of the bathroom so you can listen to the radio while you take a shower. They also had heated mirrors, so when the bathroom gets steamy the mirrors don't fog up. We got a rate of just under $200 a night from Expedia when we went in 2004.
Oh, and what you've heard is true- the Guinness is WAY better there than anywhere else on earth.