I don't recommend 27" @1080p, it's simply too few pixels to cover the 27" im my opinion. 23" and 24" is the sweet spot, 23" being cheaper. Depending on your budget and needs connection wise:
Asus VN248H 23.8" £165 (2 x HDMI, VGA, comes with HDMI cable)
Asus PB238Q 23.0" £188 (DP, HDMI, DVI, VGA, height adjustment and swivel)
Asus PA238Q 23.0" £205
Dell U2412M 60Hz 24.0" £205 (DP, DVI, VGA, height adjustment, no HDMI)
Dell U2312HM 23.0" £155 similar connections etc. to above slightly "worse" qualityand size but obviously cheaper as well.
Check out reviews on them and see what you like (just Google search the names, check Anandtech, TFTcentral etc.)