Ton depends on Your budget. iphone 4 will not be cheap. Also You need to consider whether You want touchscreen only or normal keyboard. I have bigger hands and I was pretty annoyed by the keyboard on my brother's HTC Hero. Tried on screen keyboard on an ipod Touch 3rd gen it was a bit better but I do like the slide out keyboard of my Motorola Dext.
If You are on a budget and don't really need a fancy touchscreen phone than give Sony Ericsson C905 a try, good camera, gps, wifi. Another cheap and good option would be LG Renoir, they go silly cheap for a 8mp camera phone, wifi, gps, get them for around £100 or under. Also Samsung Tocco Ultra has a touchscreen and a slide out keyboard, 8mp camera. Looks pretty good, friend at uni has one. However if You don't mind a touchscreen only, than HTC Hero go cheap now, You'll get one for around £150, has wifi, 5mp camera, gps and loads of apps from Android market.