I have been very happy with my Bostitch pneumatic nailers. I have the oiled type and have not yet tried the latest oilless variety. I have the Bostitch 16ga Finish nailer (2.5"), 18ga Brad nailer (2"), 18ga Narrow Crown Stapler (1-1/2") and their 23ga Pinner (1-3/16"). If you are buying new and wanted all of the first three (that is, minus Pinner) it is, ironically, cheaper to by the starter kit with their 6gal oilless compressor, which is how I aquired mine (Lowes). I have not had a single issue with any of these nailers and have had them for nearly 3 years now. All of these are available locally at Lowes or from numerous online vendors.
I also have Woodcraft's European EZ-Fasten 21ga Pinner/Brad Nailer (1-3/16" or 30mm) which is great when you need either stronger pins with *much* greater holding power OR you want very small 21ga brads for those small projects. I am very happy with it with one minor exception, it does not sink the pins/brads as deeply as I would like out-of-the-box, though you can grind the tip down a fraction of an inch to fix this issue, if so motivated. I use both my EZ-Fasten and my Bostitch Pinners quite regularly.
If you want the ultimate 23ga Pinner and money is really no object, Grex has a line of 23ga Pinners (available from Woodcraft and others) which can drive 23ga pins in lengths of 1-3/8", 1-3/4" or 2" depending on the Pinner model you choose. These are pretty much the Cadillacs (Festools?) of the 23ga Pinner family and are priced accordingly... I would love to have the 1-3/4" model for those occassions when 1-3/16" pins are not quite adequate.
I have recently added a new 80gal 4HP (claimed 4.5HP) air compressor to my collection, but I will be keeping the 6gal Bostitch compressor for around-the-house and mobile (e.g. my grandmother's NC cabin) jobs ... at 38lbs it is a heck of alot easier to transport than my 500+lb shop compressor!
I can't comment on the DeWalt electric nailers another poster mentioned, but my past experiences with other electric nailers and staplers has always been very disappointing by comparision... lots of half driven nails and staples that still required a traditional hammer and nail set to finish the job. Obviously, others have apparently had better fortune than I (or maybe the DeWalts are just that much better than the other's I've tried... hard to say).
HTH
Tip: For the Bostitch 23ga Pinner, I have found that the Grex and Porter Cable 23ga pins (1/2" to 1-3/16", minus 3/4") fit this Pinner better than Bostitch's own -- with the exception of the 3/4" size for which the Grex brand are 1mm oversized and the Bostitch 3/4" pins fit perfectly. Grex pins are available from Woodcraft and Amazon, as well as other online vendors.