Sallins is just a dormitory town - you might as well be in Lucan / Swords. Nothing wrong with Sallins, just loads of houses and apartments, with no real centre to the town
Clane is very nice, but a little inaccessible i.e. no train service
Kildare is, I think, an excellent area to buy in for FTBs - considering that it is 25 miles from Dublin, with Arrow and bus connections, and the new M7 to be opened in Sept, it's much better value than people would think. you can still get 3 bed semis for c€240-€250k. Also the shopping mall and Tesco will help improve the town. However I agree with former postings, that it needs a little more gentrification, and is probably slightly ahead of its time (Ditto for Monasterevin)
I'm surprised no-one has suggested Newbridge, right now it's impossible to get property in Newbridge. It has always been the main town for shopping in Kildare, sits on the River Liffey, right beside the Curragh, has greyhound stadium, Kildare County soccer club, St. Conleth's Park (GAA) number of golf clubs, has the same Arrow service as Kildare, and a number of private and public bus services run from Newbridge to Dublin. Nightlife isn't bad, and it's quite an easy town to move around in (once the Whitewater building works were completed, that is!)
At the risk of getting my head chewed off, I think that Naas is well-overrated. It has some very nice pubs & restaraunts, but has little shopping. You have to go to Sallins to pick up the train to Dublin ( that's why so many houses and apartments have sprung up in Sallins), it has very few sporting amenities (Naas rugby club, couple of golf courses), and the main street is a nightmare to drive through morning and night. I have noticed that the price differential for property between Naas and Newbridge has narrowed considerably over the past 6-12 months, they are almost equal at this point - possibly because all new developments are being built in Sallins direction. I believe there is a tendency for people to retain a 'snob' value with Naas, which now seems to be based on somewhat suspect rationale.
I have little or no knowledge of Celbridge and Leixlip, other than they are very built up. Maynooth is nice, historical, university town. The last place I would mention would be Athy, but this is quite a distance from Dublin (40miles), no train service yet to Dublin, very reasonable for property prices, but traffic in the centre of Athy is almost worse than Dublin city centre traffic (and that's what Athy people would say)